Dynamic contrast-enhanced perfusion processing for neuroradiologists: model-dependent analysis may not be necessary for determining recurrent high-grade glioma versus treatment effect.

BACKGROUND AND PURPOSE: Dynamic contrast-enhanced perfusion MR imaging has proved useful in determining whether a contrast-enhancing lesion is secondary to recurrent glial tumor or is treatment-related. In this article, we explore the best method for dynamic contrast-enhanced data analysis. MATERIALS AND METHODS: We retrospectively reviewed 24 patients who met the following conditions: 1) had at least an initial treatment of a glioma, 2) underwent a half-dose contrast agent (0.05-mmol/kg) diagnostic-quality dynamic contrast-enhanced perfusion study for an enhancing lesion, and 3) had a diagnosis by pathology within 30 days of imaging. The dynamic contrast-enhanced data were processed by using model-dependent analysis (nordicICE) using a 2-compartment model and model-independent signal intensity with time. Multiple methods of determining the vascular input function and numerous perfusion parameters were tested in comparison with a pathologic diagnosis. RESULTS: The best accuracy (88%) with good correlation compared with pathology (P = .005) was obtained by using a novel, model-independent signal-intensity measurement derived from a brief integration beginning after the initial washout and by using the vascular input function from the superior sagittal sinus for normalization. Modeled parameters, such as mean endothelial transfer constant > 0.05 minutes(-1), correlated (P = .002) but did not reach a diagnostic accuracy equivalent to the model-independent parameter. CONCLUSIONS: A novel model-independent dynamic contrast-enhanced analysis method showed diagnostic equivalency to more complex model-dependent methods. Having a brief integration after the first pass of contrast may diminish the effects of partial volume macroscopic vessels and slow progressive enhancement characteristic of necrosis. The simple modeling is technique- and observer-dependent but is less time-consuming.

Phase II study of accelerated fractionation radiation therapy with carboplatin followed by PCV chemotherapy for the treatment of anaplastic gliomas.

PURPOSE: To conduct a Phase II one-arm study to evaluate the long-term efficacy and safety of accelerated fractionated radiotherapy combined with i.v. carboplatin for patients with previously untreated anaplastic gliomas. METHODS AND MATERIALS: Between 1988 and 1992, 90 patients received 1.9-2.0-Gy radiation 3 times a day with 2-h infusions of 33 g/m(2) carboplatin for two 5-day cycles separated by 2 weeks. After radiotherapy, patients received procarbazine, lomustine (CCNU), and vincristine (PCV) for 1 year or until the tumor progressed. RESULTS: Ninety patients were evaluable for analysis. Histologically, 69 had anaplastic astrocytoma; 14, anaplastic oligoastrocytoma; and 7, anaplastic oligodendroglioma. Gross total resection was performed in 20 (22%), subtotal resection in 45 (50%), and biopsy in 25 (28%); reoperation (total or subtotal resection) was performed in 50 (56%) patients. A multivariate analysis showed that a younger age (p = 0.026), Karnofsky performance score (KPS; p = 0.009), and brain necrosis (p = 0.0002) were predictive of a better survival. Results from analysis of extent of surgery (biopsy, subtotal resection, gross total resection) approached significance (p = 0.058). Radiation dose, irradiated tumor volume, and techniques used (boost and fields) were not significant variables. The median survival (MS) of all anaplastic glioma patients was 28.1 months; for anaplastic astrocytoma patients, MS was 28.7 months and 40.8 months for the combined anaplastic oligodendroglioma/oligoastrocytoma patients. Long-term survival occurred in 25% of anaplastic glioma patients who were alive 8.6 years after treatment was initiated. Treatment-induced necrosis was documented by surgery or autopsy in 19 (21%) patients; 21 (23%) had a mixed pattern of necrosis and tumor; and an additional 13 (14%) patients who did not have surgical or autopsy demonstration of predominant radiation necrosis had magnetic resonance imaging (MRI) evidence of radiation necrosis. Serious clinical neurologic deterioration and/or dementia requiring full-time caregiver attention were observed in 9 (10%) patients. CONCLUSION: When comparable selection criteria are applied, the rate of MS in this study is inferior to results attainable with current radiation and chemotherapy approaches, although the rates of long-term survival are comparable. Theoretically, patients failing therapy and dying earlier than anticipated may be because of excessive central nervous system (CNS) toxicity resulting from the combination of accelerated fractionated irradiation, intensive carboplatin chemotherapy before each radiation fraction, and postirradiation PCV chemotherapy. On the other hand, patients with treatment-induced necrosis survived significantly longer than patients who did not demonstrate MRI or histologic evidence of necrosis (MS, 106 months vs. 18-33 months).

Post-epidural analgesia spinal cord infarction: MRI correlation.

Permanent neurological deficits after epidural analgesia are rare, but have long been believed to be caused by cord ischaemia when no obvious cause is demonstrable. The mechanisms of this injury are uncertain, but a literature review suggests important risk factors. We report a first case of extensive spinal cord infarction confirmed by magnetic resonance imaging (MRI) following post-thoracotomy epidural analgesia and review the literature to explain the mechanism underlying this devastating complication.

Choroid plexus cyst and chordoid glioma. Report of two cases.

Several types of mass lesions may occur in the third and lateral ventricles. Typically they arise from the lining of the ventricular cavity or from contiguous structures, by extension into the ventricle. The authors describe two patients, each of whom presented with a different rare lesion of the ventricular system. The first was a 53-year-old woman with a history of hypertension who sustained a blunt traumatic injury to the occipital region and subsequently developed a progressively worsening right-sided headache. Radiological examinations over the next 2 years revealed an enlarged right lateral ventricle and, ultimately, a choroid plexus cyst in its anterior and middle third, near the foramen of Monro, which is a rare location for these lesions. The cyst was removed en bloc, and follow-up examinations showed a significant improvement in her headache and a minimal differences in size between right and left ventricles. The authors also describe a 57-year-old man with hypertension, diabetes mellitus, and an old mycardial infarct, who presented to an outside institution with a progressively worsening headache, generalized malaise, and loss of olfactory sensation. Diagnostic imaging revealed a 1.5-cm oval lesion centered in the lamina terminalis region, an open craniotomy was performed, and evaluation of a biopsy sample demonstrated the mass to be a chordoid glioma of the third ventricle, a recently described glioma subtype. Two days after surgery, he suffered a left parietal stroke and an anterior mycardial infarction. After convalescing, he presented to The University of Texas M. D. Anderson Cancer Center for radiotherapy and follow up; 7 months later he was readmitted complaining of headache, short-term memory loss, and worsening confusion and disorientation. Neuroimaging revealed progression of the tumor (now 2 cm in diameter), which was removed by gross-total resection. His headache resolved immediately, and 2 months later his only complaint was of episodes of confusion. Three weeks later he died of a massive myocardial infarction. These two patients represent the sixth case of an adult with a choroid plexus cyst in the anterior lateral ventricle and the 19th case of an adult with a chordoid glioma of the third ventricle, respectively.

Evolution of diagnostic neuroradiology from 1904 to 1999.

Neuroradiology began in the early 1900s soon after Roentgen discovered x rays, with the use of skull radiographs to evaluate brain tumors. This was followed by the development of ventriculography in 1918, pneumoencephalography in 1919, and arteriography in 1927. In the beginning, air studies were the primary modality, but this technique was supplanted by angiography in the 1950s and 1960s. The first full-time neuroradiologist in the United States was Cornelius G. Dyke at the New York Neurological Institute in 1930. Neuroradiology took a firm hold as a specialty in the early 1960s when Dr Juan M. Taveras brought together fourteen neuroradiologists from the United States and Canada to establish the nucleus of what was to become the American Society of Neuroradiology, or ASNR. This society's initial goals were to perform research and to advance knowledge within the specialty. Neuroradiologists initially were able to diagnose vascular disease, infections, tumors, trauma, and alterations in cerebrospinal fluid flow, because the brain structure was invisible. Neuroradiology was forever changed with computed tomography (CT) because the brain structure became visible. Soon thereafter, magnetic resonance (MR) imaging was developed, and it not only provided anatomic but also made possible vascular and physiologic functional imaging.

Malignant gliomas: MR imaging spectrum of radiation therapy- and chemotherapy-induced necrosis of the brain after treatment.

PURPOSE: To describe both the common and less frequently encountered magnetic resonance (MR) imaging features of radiation therapy- and chemotherapy-induced brain injury, with particular emphasis on radiation necrosis. MATERIALS AND METHODS: A cohort of 148 adult patients underwent surgical resection of malignant brain (glial) tumors and were subsequently entered into a research protocol that consisted of accelerated radiation therapy with carboplatin followed by chemotherapy with procarbazine, lomustine, and vincristine. Patients typically underwent sequential MR imaging at 6-8-week intervals during the 1st year and at 3-6-month intervals during subsequent years. In all patients, histopathologic confirmation of lesion composition was performed by board-certified neuropathologists. RESULTS: The patients exhibited different types of MR imaging-detected abnormalities of the brain: pure radiation necrosis in 20 patients, a mixture of predominantly radiation necrosis with limited recurrent and/or residual tumor (less than 20% of resected tissue) in 16 patients, radiation necrosis of the cranial nerves and/or their pathways in two patients, radiation-induced enhancement of the white matter in 52 patients, and radiation-induced enhancement of the cortex in nine patients. CONCLUSION: The frequent diagnostic dilemma of recurrent neoplasm versus radiation necrosis is addressed in this study through a description of the varying spatial and temporal patterns of radiation necrosis at MR imaging.

Intracranial leptomeningeal metastases: comparison of depiction at FLAIR and contrast-enhanced MR imaging.

PURPOSE: To compare contrast material-enhanced T1-weighted and fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) images in depicting leptomeningeal metastases. MATERIALS AND METHODS: Malignant lesions detected at cytologic examination of cerebrospinal fluid in 70 patients were reviewed. There were 58 studies in which both FLAIR and contrast-enhanced T1-weighted spin-echo MR images were available. A senior neuroradiologist reviewed the images from each sequence individually and separately for signs of leptomeningeal metastases and assigned a diagnostic rating of positive, indeterminate, or negative. RESULTS: Leptomeningeal metastases were depicted in 38 cases on contrast-enhanced T1-weighted spin-echo images and in 20 cases on FLAIR images. In three cases, leptomeningeal metastases were detected by using only FLAIR images. In 20 cases, leptomeningeal metastases were detected by using only contrast-enhanced T1-weighted spin-echo images. FLAIR imaging has a sensitivity of 34% for cytologically proved leptomeningeal metastases. Gadolinium-enhanced MR imaging has a sensitivity of 66%. CONCLUSION: Used alone, contrast-enhanced T1-weighted images are better than FLAIR images for detecting leptomeningeal metastases. This is particularly true for cases in which leptomeningeal metastases manifest primarily or solely as cranial nerve involvement.

Magnetic resonance imaging in patients with central nervous system pathology: a comparison of OptiMARK (Gd-DTPA-BMEA) and Magnevist (Gd-DTPA).

RATIONALE AND OBJECTIVES: The objective of the two pivotal phase 3 studies was to evaluate the safety and efficacy of OptiMARK (Gd-DTPA-bis(methoxyethylamide) [Gd-DTPA-BMEA]) compared with Magnevist (Gd-DTPA) in magnetic resonance imaging of the central nervous system. METHODS: Two multicenter, randomized, double-blind, parallel group studies were conducted in 395 patients with known or suspected central nervous system pathology. Subjects were randomized to receive a single 0.1 mmol/kg intravenous injection of either Gd-DTPA-BMEA or Gd-DTPA. The safety of Gd-DTPA-BMEA and Gd-DTPA was monitored for up to 72 hours after study drug administration. Precontrast and postcontrast administration magnetic resonance scans were acquired using identical imaging planes and techniques. RESULTS: No deaths or unexpected adverse events were reported in either group. A comparison of adverse events by intensity and relation demonstrated no statistically significant differences between the two groups. Gd-DTPA-BMEA and Gd-DTPA were equivalent with respect to confidence in diagnosis, conspicuity, and border delineation. CONCLUSIONS: Gd-DTPA-BMEA and Gd-DTPA demonstrated comparable efficacy profiles, and the safety profiles were considered similar.

Quantitative morphology of the corpus callosum in children with neurofibromatosis and attention-deficit hyperactivity disorder.

Neurofibromatosis-1 is a common autosomal-dominant genetic disorder associated with numerous physical anomalies and an increased incidence of attention-deficit hyperactivity disorder (ADHD). Studies of children with idiopathic ADHD have suggested a link between corpus callosum size and symptom severity. This study examines the contribution of corpus callosum morphology to symptoms of ADHD in children with neurofibromatosis. Eighteen control subjects and 36 children with neurofibromatosis underwent magnetic resonance imaging of the brain. Twelve subjects with neurofibromatosis had evidence of ADHD and 24 did not. Subjects with neurofibromatosis had significantly larger total corpus callosum area and significantly larger regional measurements in three of seven areas. However, there were no differences between the neurofibromatosis alone and neurofibromatosis plus ADHD groups. Increased severity of attention problems was associated with smaller total callosal areas. These results suggest that some features of ADHD in children with neurofibromatosis could be linked to quantifiable differences in brain morphology, but the nature of the genetic mutation in neurofibromatosis suggests that neurochemical effects also could be important.

Brain volume in children with neurofibromatosis type 1: relation to neuropsychological status.

OBJECTIVE: To determine characteristics of brain morphology in children and adolescents with neurofibromatosis type 1 and relate these characteristics to neuropsychological functioning. BACKGROUND: Neurofibromatosis type 1 is associated with numerous CNS abnormalities and cognitive impairment. Abnormal high signal intensity visible on brain MRI, brain tumors, and macrocephaly are common. Research into links between neuroanatomic and cognitive features has been inconclusive. METHODS: Fifty-two children and adolescents with neurofibromatosis type 1 were compared with 19 control subjects on several quantitative neuroanatomic and neuropsychological measures. RESULTS: Total brain volume, especially gray matter, was significantly greater for neurofibromatosis type 1 subjects than the control subjects. Group differences in the ratio of gray matter to white matter were more prominent in younger than in older subjects. Volume of gray matter in the subjects with neurofibromatosis type 1 was related to their degree of learning disability. Corpus callosum size was significantly larger for subjects in the neurofibromatosis type 1 group, and diminished performance on measures of academic achievement and visual-spatial and motor skills were associated with greater regional corpus callosum size. CONCLUSIONS: Neuroanatomic morphology and the developmental pattern of gray matter and white matter in subjects with neurofibromatosis type 1 differed from in control subjects. Some of these differences are related to the neuropsychological status of the neurofibromatosis type 1 group. We propose that delayed developmental apoptosis results in macrocephaly and a delay in the development of appropriate neuronal connections in children with neurofibromatosis type 1. We further propose that these morphologic delays are related to the cognitive profile of neurofibromatosis type 1.

Magnetic resonance imaging of benign spinal lesions simulating metastasis: role of diffusion-weighted imaging.

In an attempt to avoid unnecessary therapy, this article demonstrates benign vertebral body lesions that mimic metastatic disease in cancer patients with back pain. The magnetic resonance imaging features that aid in differential diagnosis are demonstrated. In addition, the value of diffusion-weighted spinal imaging to further aid in distinguishing benign from malignant disease is described.

Identification of structural elements of the testis-specific voltage dependent calcium channel that potentially regulate its biophysical properties.

Calcium influx through voltage-dependent calcium channels regulates the physiological acrosome reaction of mammalian spermatozoa. Expression of the mRNA for these voltage-dependent calcium channels and its co-ordinated translation is initiated early in rat male germ line development and continues throughout spermatogenesis. Herein, we report the complete mRNA and deduced amino acid sequence of the alpha1c pore-forming subunit of the rat testis-specific L-type calcium channel. This subunit is transcribed from the alpha1c gene, which is also expressed in brain and cardiac muscle. The cardiac- and testis-specific isoforms of the alpha1c subunit are produced by alternate splicing of the same primary transcript. The testis-specific isoform differs from that of cardiac tissue at its amino terminus and in transmembrane segments IS6, IIIS2 and IVS3, which are also dihydropyridine binding sites. In somatic tissues, segments S2 and S3 regulate channel activation while the amino terminus and segment IS6 contribute to channel inactivation kinetics. The amino terminus and IS6 segment of the testis-specific alpha1c subunit are also expressed respectively, in the brain and in smooth muscle from lung where they alter the electrophysiological characteristics of the subunit to produce relatively slow inactivation kinetics. These findings provide a molecular explanation for the detection by others, by patch clamp analysis, of T-type calcium currents in immature spermatogenic cells and of atypical L-type calcium currents in mature spermatozoa.

Alternative splicing of exons in the alpha1 subunit of the rat testis L-type voltage-dependent calcium channel generates germ line-specific dihydropyridine binding sites.

Cell-specific isoforms of the alpha1 subunit of the L-type voltage-dependent calcium channel (VDCC) have unique pharmacological reactivities. Prior sequence analysis of nucleotide bases 3908-6077 of the VDCC alpha1 subunit expressed in rat testis differed from cardiac sequences only in a 84 base pair region corresponding to exons 31/32 encoding a putative dihydropyridine binding region. We now report that sequence analysis of bases 3048-3936 identifies a second difference between the rat testis and rat cardiac alpha1 sequence in a 60 base pair region corresponding to exons 21/22 and encoding another putative dihydropyridine binding site. Variable VDCC exons 21/22 and 31/32 and their linking introns were sequenced using genomic DNA from rat lung as template, providing evidence that the rat testis and cardiac alpha1 isoforms are products of the same gene. Reverse transcription in-situ polymerase chain reaction (PCR) with frozen sections of rat testis was carried out with primers identifying the testis-specific exon 32 of the VDCC alpha1 subunit. PCR products were confined to seminiferous tubules and were associated with the germ cell lineage from Type A spermatogonia to mature spermatozoa. Close coupling of testis alpha1 VDCC gene transcription and translation was established by in-situ immunolabelling of serial frozen sections with a monoclonal antibody (IIF7) directed against epitopes on rabbit skeletal muscle L-type VDCC alpha1. Western blot analysis of rat proteins extracted from heart, skeletal muscle, testis and spermatozoa which were reactive with the IIF7 antibody detected primarily 175-220 kDa proteins in the size range of VDCC. These data unequivocally demonstrate that an L-type VDCC is expressed in rat testis and that VDCC isoforms from rat testis and heart differ in deduced amino acid composition in and around potential binding sites for calcium channel blocking drugs such as the dihydropyridines.

The significance of lack of MR contrast enhancement of supratentorial brain tumors in adults: histopathological evaluation of a series.

BACKGROUND: To correlate magnetic resonance imaging (MRI) findings of non-enhancement of supratentorial brain neoplasms in adults with histopathologic findings. METHODS: Forty adult patients whose preoperative MRI studies demonstrated a non-enhancing supratentorial brain neoplasm were identified retrospectively. Biopsy material for all patients was then reviewed by a board-certified neuropathologist. RESULTS: Histopathologic examination identified 24 (60%) low-grade gliomas: 4 (10%) low-grade astrocytomas, 10 (25%) low-grade gliomas (not further classified), 8 (20%) low-grade oligodendrogliomas, and 2 (5%) low-grade mixed oligoastrocytomas. However, 16 (40%) nonenhancing lesions were classified as anaplastic gliomas: 12 (30%) anaplastic astrocytomas, 1 (2.5%) anaplastic mixed oligoastrocytoma, 1 (2.5%) anaplastic oligodendroglioma, and 2 (5%) anaplastic infiltrating gliomas of indeterminate subtype. CONCLUSION: Non-enhancement of supratentorial brain neoplasms in adults does not equate with low-grade malignancy. This fact should be taken into account when biopsy and treatment are being planned in patients with nonenhancing brain tumors. More aggressive and/or surgical therapy might be indicated for such lesions, particularly those in the nondominant hemisphere or nonmotor areas.

Correlation between dynamic MRI and outcome in patients with malignant gliomas.

We assessed the correlation between dynamic MRI results and clinical outcomes in patients with malignant gliomas. Rapid serial MRIs were obtained after bolus injection of gadolinium that resulted in an initial fast uptake followed by a slow uptake of contrast. The maximum rate of uptake and delayed rate of uptake were correlated with survival and prognostic covariates such as age and histology. In 121 subjects, higher maximum uptake rates, 3.6 signal intensity units per second or greater, were associated with shorter survival (p = 0.0066). The correlation of delayed rate of uptake with survival was less significant. After adjusting for age, histology, and Karnofsky performance score, the maximum rate of uptake remained more significantly correlated with survival than the delayed rate of uptake. Thirty-one patients had surgery within 1 month of dynamic MRI, and those with glioblastoma multiforme or anaplastic gliomas had higher maximum rates of uptake than those with pure necrosis or mixed tumor and necrosis (p = 0.022). No correlation between delayed rate of uptake and histology was seen in this group of patients. Our results suggest that the maximum rate of uptake in dynamic MRI can be a prognostic measure for patients with malignant gliomas. Further prospective study is needed to assess the utility of this technique for evaluating brain tumors.

Dynamic imaging of intracranial lesions using fast spin-echo imaging: differentiation of brain tumors and treatment effects.

The purpose of this study was to develop a technique for differentiating between recurrent brain tumors and treatment-related changes, such as radiation necrosis, using dynamic MRI. Ninety-five patients with intracranial mass lesions were evaluated using T1-weighted fast spin-echo (FSE) MRI at 1.5 T. Pathologies included treatment-related changes (n = 32), primary tumors (n = 41), metastatic tumors (n = 5), meningiomas (n = 4), and mixed primary/treatment related changes (n = 13). Signal enhancement-time curves were analyzed by fitting to a sigmoidal-exponential function. Maximal enhancement rates were calculated as the first derivative of the fitted curve. Based on the maximal enhancement rates, treatment-related changes could be differentiated from primary tumors, metastatic tumors, and meningiomas at the P < .05 confidence level. Lesions of mixed tumor and treatment-related change had intermediate values. Dynamic MRI can be used to differentiate treatment-related changes from primary tumors in previously treated patient populations based on maximal enhancement rates. Individual case studies demonstrate the clinical significance of these findings.

A second look at unenhanced spinal magnetic resonance imaging of malignant leptomeningeal disease.

The purpose of this study is to evaluate the use of unenhanced magnetic resonance (MR) imaging in identifying malignant leptomeningeal disease (MLD). Included in this study were fifty patients with evidence of leptomeningeal enhancement on post-gadolinium MR images and with cytological confirmation of MLD. Unenhanced, T1-weighted spin-echo (SE) MR images of the spine were analyzed for loss of cerebrospinal fluid (CSF) clarity, poor definition of the conus medullaris, thickened and clumped nerve roots, and nodules. Patterns of leptomeningeal enhancement on post-gadolinium, T1-weighted SE images were noted. Findings of MLD on unenhanced MR images were observed in 41 (85%) of 48 studies of the lumbar spine, 10 (50%) of 20 studies of the thoracic spine, and two (33%) of six studies of the cervical spine. In the lumbar spine, thickened and clumped nerve roots, poor definition of the conus medullaris, loss of CSF clarity, and nodules were observed with decreasing frequency. The signs of MLD on unenhanced images of the cervicothoracic spine included nodules and clouding of CSF. Patterns of leptomeningeal enhancement included linear, linear/nodular, nodular, enhancement of nerve roots, and stacking, with tumor filling the lumbosacral canal. Findings of MLD were present on 73% of the unenhanced MR images of the spine. Recognition of MLD on unenhanced MR images can guide the appropriate work-up and therapeutic approach.

Magnetic resonance imaging of the central nervous system of the rhesus monkey.

The purpose of the study reported here was to document the ability of magnetic resonance imaging to depict the imaging characteristics of normal structures within the central nervous system of adult rhesus monkeys. The head and the cervical and thoracic parts of the spinal cord of two rhesus monkeys were imaged in a clinical 1.5-T whole-body imager. Specific images were selected, and some notable structures were identified. Results of this study document the usefulness of MRI as an expeditious, noninvasive research and diagnostic imaging technique and illustrates the normal magnetic resonance signal patterns of the brain and spinal cord in rhesus monkeys.

Isolation and characterization of the primary structure of testis-specific L-type calcium channel: implications for contraception.

Therapeutic administration of calcium channel-blocking medications has been correlated with reduced mannose receptor expression and iatrogenic human male infertility. In this report, we investigate whether the pharmacological activity of dihydropyridines, which block calcium influx through voltage-dependent calcium channels, contributes to the production of an infertile state. An influx of extracellular calcium is an absolute requirement for the initiation of a progesterone-stimulated acrosome reaction by human spermatozoa. To determine whether dihydropyridines could inhibit progesterone-induced acrosome loss, we have studied a protein expressed in rat and human spermatozoa which is related both antigenically and by cDNA sequence to the alpha 1 subunit of the rat cardiac muscle voltage-dependent calcium channel, which forms the pore of the channel. Using reverse transcription-polymerase chain reaction, we have isolated a 2169 base clone from rat testis mRNA whose sequence was largely identical to that of the alpha 1 subunit of the rat cardiac muscle calcium channel, but had an 84 base change, attributable to splicing and alternate exon usage. This change inserts a peptide cassette encoding an amphipathic membrane-spanning helix that constitutes part of the ionic pore of the skeletal muscle calcium channel regulating the kinetics of activation of the calcium channel and may serve as an intramembrane dihydropyridine binding site. In parallel, human spermatozoa from fertile donors were exposed to nifedipine in vitro. Nifedipine inhibited progesterone-stimulated calcium influx and subsequent acrosome reactions in human spermatozoa at concentrations effective in excitable cells, but required a prolonged time to do so. In contrast, progesterone ligand binding was unaffected by nifedipine treatment. These data demonstrate that human spermatozoa express an L-type calcium channel which is responsive to nifedipine. Assuming sperm calcium transport pathways are highly conserved, the slow kinetics by which the blockade of the human sperm channel was obtained can be correlated with alterations in channel activation and conductance associated with isoform diversity generated by alternate splicing as observed in the rat. These data provide unequivocal evidence for the presence of functional L-type voltage-dependent calcium channels in rat and human spermatozoa. The data also define an altered binding site for calcium entry antagonists in this channel and offer a unique target for the design of new male contraceptive agents.