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Effects of excitatory neurotransmitters on Ca 2+ channel current in smooth muscle cells isolated from guinea‐pig urinary bladder
Author(s) -
Nakayama S.
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13811.x
Subject(s) - muscarinic acetylcholine receptor , chemistry , depolarization , carbachol , biophysics , membrane potential , purinergic receptor , stimulation , patch clamp , inhibitory postsynaptic potential , voltage clamp , endocrinology , excitatory postsynaptic potential , medicine , receptor , biology , biochemistry
1 A whole‐cell voltage clamp technique was used to examine the effects of purinoceptor and muscarinic receptor agonists on voltage‐sensitive Ca 2+ channels in guinea‐pig isolated urinary bladder cells. 2 When the cell membrane was clamped at the holding potential, rapid application of ATP elicited a large inward current in normal solution containing 2.5 m m Ca 2+ , and reduced the subsequent Ca 2+ channel current evoked by a depolarizing pulse (0 mV). Carbachol (CCh) elicited little membrane current, but similarly reduced the Ca 2+ current. 3 When purinoceptor agonists were rapidly applied during conditioning depolarizations at +80 mV, an outward current was elicited, and the Ca 2+ channel current evoked by the subsequent test potential of 0 mV was not affected. Application of CCh at +80 mV also elicited an outward current, but it reduced the subsequently evoked Ca 2+ current. 4 The inhibitory effect of muscarinic agonists on the Ca 2+ channel current was attenuated by caffeine (10 m m ). 5 In Ca 2+ ‐free, low‐Mg 2+ solution, a Na + current flowing through voltage‐dependent Ca 2+ channels was evoked by depolarization. This current was not reduced by bath application of purinoceptor agonists (ATP and α,β‐methylene ATP). 6 These results suggest that the main effect of purinoceptor stimulation is opening of non‐selective cation channels, and that muscarinic stimulation triggers Ca 2+ release from intracellular stores. Voltage‐sensitive Ca 2+ channels are inactivated through an increase in intracellular Ca 2+ induced by either activation of purinoceptor or muscarinic receptors.