Force, membrane potential and cytoplasmic Ca2+ responses to cyclic nucleotides in rat anococcygeus muscle.
Eur J Pharmacol
; 362(2-3): 183-92, 1998 Dec 04.
Article
in En
| MEDLINE
| ID: mdl-9874169
ABSTRACT
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.
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Collection:
01-internacional
Database:
MEDLINE
Main subject:
Calcium
/
Membrane Potentials
/
Muscle, Smooth
/
Nucleotides, Cyclic
Limits:
Animals
Language:
En
Journal:
Eur J Pharmacol
Year:
1998
Document type:
Article
Affiliation country:
Australia