Generation of slow-wave-type action potentials in canine colon smooth muscle involves a non-L-type Ca2+ conductance.
1. The hypothesis was addressed that a non-L-type calcium conductance is involved in the generation of the initial part of the slow-wave-type action potential in the canine colon. 2. In the absence of a sodium and chloride gradient (NaCl replaced by glucamine), and in the presence of nitrendipine (in 'glucamine-nitrendipine' Krebs solution), a major portion of the upstroke potential of the slow wave persists at unchanged frequency. 3. In 'glucamine-nitrendipine' Krebs solution, the rate of rise and amplitude of the upstroke potential is reduced by removal of extracellular calcium in a concentration-dependent manner. 4. The rate of rise and the amplitude of the upstroke potential is in a concentration-dependent manner reduced by Ni2+ greater than Cd2+ greater than Co2+ greater than Mg2+. 5. In 'glucamine-nitrendipine' Krebs solution, Ba2+ cannot replace Ca2+ in the generation of the upstroke potential. 6. Positive evidence was obtained for the hypothesis that a non-L-type calcium conductance is involved in the initiation of the slow-wave-type action potential in colonic smooth muscle.
Huizinga
J D
JD
Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Farraway
L
L
Den Hertog
A
A
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003106:Colon / Q000502:physiology*; D004285:Dogs; D005260:Female; D007473:Ion Channels / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology
D007473:Ion Channels; D002104:Cadmium; D001464:Barium; D003035:Cobalt; D009532:Nickel; D008274:Magnesium; D002118:Calcium