Potentiation of nerve-induced bladder contractions after calcium channel blockade.
The potentiation of nerve-induced bladder contractions (NIC) by tetraethylammonium chloride (TEA), K+, or carbachol could result from a greater Ca2+ entry through Ca2+ channels in the muscle or from a greater release of transmitter by nerve terminals. Contractions of equal magnitude by the rat urinary bladder in vitro were initiated by carbachol, K+, or transmural stimulation of urinary bladder motor nerves at 1 Hz. Contractions elicited by K+ or carbachol were drastically reduced by verapamil (0.5 microM), but NICs were unaffected. Thus the role of Ca2+ channels in NICs seems uncertain. NICs are potentiated approximately 50% by K+ (15 mM), carbachol (0.5 microM), or 4-aminopyridine (0.2 mM) and over twofold by TEA (5 mM). Although verapamil (1-5 microM) reduced NICs in a dose-dependent relation, potentiation by each compound was the same. Thus Ca2+ channels probably play no role in potentiation. The resistance of the bladder to distention reflects its viscoelasticity and is Ca2+ sensitive. Because viscoelasticity was decreased by verapamil coincident with the reduction in NICs, both may result from lowered intracellular Ca2+ (Cai2+). However, because the potentiating compounds failed to restore bladder viscoelasticity, they probably did not elevate Cai2+. Therefore, in verapamil-treated preparations potentiation is most probably caused by an enhancement of transmitter release.
Carpenter
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D004548:Elasticity; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013268:Stimulation, Chemical; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000294:innervation*; D014700:Verapamil / Q000494:pharmacology*
D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D002217:Carbachol; D014700:Verapamil; D011188:Potassium; D002118:Calcium