Force, membrane potential and cytoplasmic Ca2+ responses to cyclic nucleotides in rat anococcygeus muscle.
Simultaneous recordings of membrane potential and force, and cytoplasmic calcium ([Ca2+]i) and force were made in rat anococcygeus to determine whether membrane hyperpolarisation plays a role in cyclic nucleotide-induced relaxation. In the presence of phenylephrine (0.2 microM), which evoked sustained contraction, an elevation in [Ca2+]i, and depolarisation, nitroprusside (5 microM) caused 96+/-3% relaxation, 77+/-3% decrease in suprabasal [Ca2+]i, and 16+/-2 mV hyperpolarisation. Forskolin (1 microM) caused 98+/-1% relaxation, 92+/-2% decrease in suprabasal [Ca2+]i, and 18+/-1 mV hyperpolarisation. These responses persisted in the presence of a variety of K+ channel blockers or in ouabain. The decrease in [Ca2+]i preceded the commencement of relaxation whereas the onset of hyperpolarisation lagged behind. Thus, cyclic nucleotide-mediated relaxation in rat anococcygeus is not dependent on hyperpolarisation mediated by the opening of K+ channels. Rather, it is suggested that the decrease in [Ca2+]i gives rise to hyperpolarisation, which reflects a decline in the Ca2+ dependent conductance(s) activated by phenylephrine.
Raymond
G L
GL
Department of Physiology, Monash University, Clayton, Australia.
Tonta
M A
MA
Parkington
H C
HC
Wendt
I R
IR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004347:Drug Interactions; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology; D009712:Nucleotides, Cyclic / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D009712:Nucleotides, Cyclic; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D005576:Colforsin; D010656:Phenylephrine; D002118:Calcium