Nesin V. The properties of Ca2+-activated and ATP-induced potassium currents of smooth muscle cell membrane of guinea-pig taenia caeci

The dissertation is devoted to pharmacological and biophysical investigations of the components of outward transmembrane ionic current in single smooth muscle cells isolated from guinea-pig taenia caeci and clarifying the mechanisms of the action of ATP as an inhibitory neurotransmitter in guinea-pig gastrointestinal tract. Different components of the net outward current were separated using patch-clamp technique. It was shown that outward potassium current was inhibited at 50 % by application of 1 mM of non-selective potassium channels blocker TEA and at 40 % - by application of 100 nM of high-specific BK channels blocker paxilline. About 10 % of the net outward current was suppressed by application of 50 mkM of SK channels and nicotinic cholinergic receptors d-tubocurarine (d-TK). Effects of these blockers on the spontaneous transient outward currents (STOCs) were also studied. It was shown that STOCs could be divided on two groups depending on its characteristics. Large STOCs are sensitive to the blocking action of TEA and paxilline and thereby are likely to determined by BK channels activity. Mini STOCs are sensitive to d-TK which is an evidence for involving of SK channels. The studying of STOCs during application of ATP revealed that the main role in purinoergic inhibition is devoted to SK channels as a mainstream mechanism of SMC membrane hyperpolarization. The investigation of the intracellular pathways of inhibition induced by an activation of SMC purinoergic receptors testified that a blocker of IP3 receptor 2-APB (30 mM) decreased frequency mini STOCs and did not alter large STOCs. In result , we can assume that origin of small amplitude STOCs is due to calcium release from sarcoplasmic reticulum of SMC through IP3 receptors. The additional application of ATP(100 mM) along with 2-APB as well as with U73122 (blocker of phospholipase C) did not invoke increase in frequency and amplitude of STOCs. Thus, ATP induced STOCs in SMC of taenia caeci are generated due to enhancement of flux of calcium caused by activation of PLC and, consequently, increasing production of IP3 which, in turn, leads to activation of IP3 sensitive receptors of sarcoplasmic reticulum membrane.