Abstract
Using a sucrose-bridge technique, we studied electrical and mechanical responses of smooth muscle ring strips of the rabbit main pulmonary artery to applications of blockers of voltage-operated (including Ca2+-dependent) K+ channels, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), as well to application of nitric oxide (NO); nitroglycerin (NG) was used as a donor of the latter. All experiments were carried out under conditions of blockade of the adreno- and cholinoreceptors in the preparation. Both TEA and 4-AP evoked dose-dependent effects: depolarization of smooth muscle cells (SMC) and their contraction. Simultaneous addition of TEA and 4-AP to the normal superfusate (Krebs solution) resulted in intensification of depolarization and initiated generation of action potentials (AP); contractions became rather intensive and possessed a tetanic pattern. Addition of NG to TEA- and 4-AP-containing Krebs solution effectively suppressed AP generation and contractions, whereas the depolarization level underwent only mild modifications. These findings show that Ca2+-dependent high-conductance K+ channels (KCa channels) and 4-AP-sensitive voltage-operated K+ channels (KV channels) are involved in the formation of the resting membrane potential (RMP) in SMC of the rabbit main pulmonary artery. The impact of the KCa channels is greater than that of the KV channels. We suppose that the effects of NO on SMC are related to inhibition of the activity of high-threshold voltage-operated L-type Ca2+ channels and, probably, to lowering of the sensitivity of the contractile SMC apparatus to Ca2+.
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Telezhkin, V.S., Tsvilovskii, V.V., Dyskina, Y.B. et al. Effects of K+ Channel Blockers and Nitric Oxide on the Electrical and Contractile Activities of Smooth Muscles of the Rabbit Main Pulmonary Artery. Neurophysiology 33, 281–288 (2001). https://doi.org/10.1023/A:1014327728657
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DOI: https://doi.org/10.1023/A:1014327728657