Amylase release from rat parotid glands. I. General characteristics.

The involvement of calcium, ATP, and cyclic AMP-dependent protein kinase activity in the release of amylase from rat parotid glands was examined. Pretreatment of the glandular tissue in 11.25 mM Ca2+ medium potentiated the secretory responses to: dibutyryl cyclic AMP, elevation of the extracellular K+ concentration, reduction of the H+ concentration, La3+, and caffeine. Uncoupling of oxidative phosphorylation blocked release induced by dibutyryl cyclic AMP, K+, and reduction of H+, but had no effect on La3+, caffeine or tolbutamide-stimulated release. Inhibition of cyclic AMP-dependent protein kinase activity blocked only dibutyryl cyclic AMP-induced release and did not inhibit the responses to K+, reduction of H+ or caffeine. The loss of lactate dehydrogenase was used to access the integrity of the tissue during amylase release. No significant increase in the release of lactate dehydrogenase was observed during the secretory responses to: dibutyryl cyclic AMP, La3+, caffeine, or tolbutamide. Triton X-100 and ethanol increased the efflux of both amylase and lactate dehydrogenase. The differential involvement of Ca2+, ATP, and cyclic AMP-dependent protein kinase activity in amylase release induced by the various secretagogues suggests that three types of reactions are involved in the release of amylase.

Amylase release from rat parotid glands. II. Calcium kinetics.

The kinetics of 45Ca2+ uptake, efflux, and calcium potentiation of amylase release by slices of rat parotid glands were examined. Pretreatment of the tissue with 11.25 mM 45Ca2+ medium increased the total tissue 45calcium content. Lanthanum (1 mM) decreased tissue uptake, blocked the slow components of exchange and appeared to inhibit transcellular calcium movement. Neither dibutyryl cyclic AMP nor caffeine caused consistently significant effects on 45Ca2+ kinetics, or total 45calcium content. Carbamylcholine increased the initial rate of 45Ca2+ uptake, but had no effect on total uptake. Elevation of the extracellular Ca2+ concentration to 11.25 mM during stimulation of amylase release resulted in an initial decrease in the rate of amylase release followed by a potentiation of release which developed slowly, requiring 40--50 min to reach the maximal response. The inability to detect release-related changes in either calcium influx or mobilization, and the lengthy times and high Ca2+ concentrations required to achieve calcium potentiation suggests that calcium does not couple amylase release.

Expression of the E2F family of transcription factors during murine development.

The E2F family of transcription factors plays a crucial role in the control of cell cycle progression and regulation of cellular proliferation, both processes fundamental to mammalian development. In the present study, we have examined the levels of expression of the six currently identified E2F proteins in murine embryos/fetuses as a function of gestational age, compared the expression of these six proteins in selected developing and adult tissues, and examined E2F expression in the embryonic murine palate, a tissue in which perturbation of proliferation is associated with induction of cleft palate. Our results indicate that: 1) multiple forms of individual E2F family members are present in embryonic, fetal and adult cells/tissues; 2) each of the six E2Fs is expressed in a tissue specific manner in both adult and embryonic/fetal organs; 3) certain forms of individual E2F family members are preferentially detected in adult tissues, whereas others are preferentially expressed in embryonic/fetal tissues; 4) expression of the various E2Fs and their isoforms follows distinct temporal patterns during murine gestation; and 5) individual E2F family members also exhibit differential patterns of temporal expression during murine palatogenesis.

Expression of the E2F and retinoblastoma families of proteins during neural differentiation.

Development of the brain is determined by a strictly orchestrated program of proliferation, migration, apoptosis, differentiation, synaptogenesis, tract formation, and myelination. The E2F family of transcription factors, whose activity and functions are regulated in large part through interactions with the retinoblastoma (Rb) family of tumor suppressor proteins, has been implicated as a key regulator of proliferation, differentiation, and apoptosis in a variety of tissues. We have examined levels of the E2F and Rb families of proteins during both brain development and neural differentiation of P19 cells, and found the expression profiles during these two processes of neural development and maturation to be quite similar, i.e., strong up-regulation of p130, pronounced down-regulation of p107, moderate up-regulation of pRb, and significant down-regulation of most species of E2F and dimerization protein (DP). However, several specific isoforms, namely a 30 kDa form of DP-2, a 57 kDa species of E2F-3, a 59 kDa form of E2F-5 and the isoforms of E2F-1 recognized by the E2F-1 (KH-95) antibody were up-regulated suggesting that these particular isoforms of E2F and DP play a tissue-specific function in differentiation and maturation of nervous tissue. The potential role of the E2F/DP family of transcription factors in aspects of neural development and differentiation are considered.

Convergence of cAMP, TGF-beta and retinoic acid signaling pathways in cells of the embryonic palate.

We have previously described bi-directional cross-talk between the retinoic acid (RA) and transforming growth factor beta (TGF-beta) signal transduction pathways in primary cultures of murine embryonic palate mesenchymal (MEPM) cells. In this paper we identify interactions between the TGF-beta1, cyclic adenosine 3', 5'-monophosphate (cAMP) and RA signaling systems. TGF-beta1 and forskolin, an activator of the cAMP pathway, inhibited RA-induced expression of RAR-beta mRNA in MEPM cells, though only TGF-beta1 inhibited RA-induced RAR-beta protein expression. Forskolin, but not TGF-beta1, abrogated RA-induced expression of a reporter construct containing 900 base pair (bp) of the RAR-beta gene promoter, transfected into MEPM cells, suggesting that this portion of the promoter contains the forskolin-responsive, but not the TGF-beta-responsive, element. Thus, a putative TGF-beta Inhibitory Element (TIE) adjacent to the retinoic acid response element (RARE) in the RAR-beta promoter is either non-functional, or requires promoter/enhancer elements not present in the promoter construct used in these experiments. These studies further clarify the complex interactions among signal transduction pathways in the regulation of retinoic acid receptor gene expression.

Lidocaine metabolism and toxicity: a laboratory experiment for dental students.

A laboratory exercise for dental students based on a modification of the classical pentobarbital sleeping-time experiment is presented. The substitution of a toxic dose of lidocaine in place of an anesthetic dose of pentobarbital allows demonstration of the same general principles of drug metabolism, i.e., induction of the hepatic drug metabolizing systems by phenobarbital, reduction of hepatic drug metabolism by liver damage or disease, or both, and the relationship between the rate of drug detoxification and the duration and intensity of drug effects. However, the use of lidocaine demonstrates its toxic and lethal actions and increases the relevance of the experience for dental students.