Modeling Perfusion Dynamics in the Skin During Iontophoresis of Vasoactive Drugs Using Single-Pulse and Multiple-Pulse Protocols.

OBJECTIVE: After iontophoresis of vasoactive drugs into the skin, a decrease in perfusion is commonly observed. We delivered vaso-active drugs by iontophoresis using different delivery protocols to study how these affect this decrease in perfusion as measured using LDF. METHODS: We measured skin perfusion during iontophoresis of (ACh), MCh, and NA using a single pulse or separate pulses at different skin sites, and during repeated delivery of ACh at the same site. RESULTS: Perfusion half-life was 6.1 (5.6-6.6) minutes for ACh and 41 (29-69) minutes for MCh (p < 0.001). The maximum response with multiple pulses of ACh iontophoresis was lower than with a single pulse, 30 (22-37) PU vs. 43 (36-50) PU, p < 0.001. Vasoconstriction to NA was more rapid with a single pulse than with multiple pulses. The perfusion half-life of ACh decreased with repeated delivery of ACh at the same site-first 16 (14-18), second 5.9 (5.1-6-9) and third 3.2 (2.9-3.5) minutes, p < 0.001. CONCLUSIONS: The drug delivery protocol affects microvascular responses to iontophoresis, possibly as a result of differences in the dynamics of local drug concentrations. Perfusion half-life may be used as a measure to quantify the rate of perfusion recovery after iontophoresis of vasoactive drugs.

Pulmonary hypertension in wild type mice and animals with genetic deficit in KCa2.3 and KCa3.1 channels.

OBJECTIVE: In vascular biology, endothelial KCa2.3 and KCa3.1 channels contribute to arterial blood pressure regulation by producing membrane hyperpolarization and smooth muscle relaxation. The role of KCa2.3 and KCa3.1 channels in the pulmonary circulation is not fully established. Using mice with genetically encoded deficit of KCa2.3 and KCa3.1 channels, this study investigated the effect of loss of the channels in hypoxia-induced pulmonary hypertension. APPROACH AND RESULT: Male wild type and KCa3.1-/-/KCa2.3T/T(+DOX) mice were exposed to chronic hypoxia for four weeks to induce pulmonary hypertension. The degree of pulmonary hypertension was evaluated by right ventricular pressure and assessment of right ventricular hypertrophy. Segments of pulmonary arteries were mounted in a wire myograph for functional studies and morphometric studies were performed on lung sections. Chronic hypoxia induced pulmonary hypertension, right ventricular hypertrophy, increased lung weight, and increased hematocrit levels in either genotype. The KCa3.1-/-/KCa2.3T/T(+DOX) mice developed structural alterations in the heart with increased right ventricular wall thickness as well as in pulmonary vessels with increased lumen size in partially- and fully-muscularized vessels and decreased wall area, not seen in wild type mice. Exposure to chronic hypoxia up-regulated the gene expression of the KCa2.3 channel by twofold in wild type mice and increased by 2.5-fold the relaxation evoked by the KCa2.3 and KCa3.1 channel activator NS309, whereas the acetylcholine-induced relaxation - sensitive to the combination of KCa2.3 and KCa3.1 channel blockers, apamin and charybdotoxin - was reduced by 2.5-fold in chronic hypoxic mice of either genotype. CONCLUSION: Despite the deficits of the KCa2.3 and KCa3.1 channels failed to change hypoxia-induced pulmonary hypertension, the up-regulation of KCa2.3-gene expression and increased NS309-induced relaxation in wild-type mice point to a novel mechanism to counteract pulmonary hypertension and to a potential therapeutic utility of KCa2.3/KCa3.1 activators for the treatment of pulmonary hypertension.

Alterations of N-3 polyunsaturated fatty acid-activated K2P channels in hypoxia-induced pulmonary hypertension.

Polyunsaturated fatty acid (PUFA)-activated two-pore domain potassium channels (K2P ) have been proposed to be expressed in the pulmonary vasculature. However, their physiological or pathophysiological roles are poorly defined. Here, we tested the hypothesis that PUFA-activated K2P are involved in pulmonary vasorelaxation and that alterations of channel expression are pathophysiologically linked to pulmonary hypertension. Expression of PUFA-activated K2P in the murine lung was investigated by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), immunohistochemistry (IHC), by patch clamp (PC) and myography. K2P -gene expression was examined in chronic hypoxic mice. qRT-PCR showed that the K2P 2.1 and K2P 6.1 were the predominantly expressed K2P in the murine lung. IHC revealed protein expression of K2P 2.1 and K2P 6.1 in the endothelium of pulmonary arteries and of K2P 6.1 in bronchial epithelium. PC showed pimozide-sensitive K2P -like K(+) -current activated by docosahexaenoic acid (DHA) in freshly isolated endothelial cells as well as DHA-induced membrane hyperpolarization. Myography on pulmonary arteries showed that DHA induced concentration-dependent instantaneous relaxations that were resistant to endothelial removal and inhibition of NO and prostacyclin synthesis and to a cocktail of blockers of calcium-activated K(+) channels but were abolished by high extracellular (30 mM) K(+) -concentration. Gene expression and protein of K2P 2.1 were not altered in chronic hypoxic mice, while K2P 6.1 was up-regulated by fourfold. In conclusion, the PUFA-activated K2P 2.1 and K2P 6.1 are expressed in murine lung and functional K2P -like channels contribute to endothelium hyperpolarization and pulmonary artery relaxation. The increased K2P 6.1-gene expression may represent a novel counter-regulatory mechanism in pulmonary hypertension and suggest that arterial K2P 2.1 and K2P 6.1 could be novel therapeutic targets.