Pharmacomechanical coupling in rat vas deferens: effects of agents that modulate intracellular release of calcium and protein kinase C activation.
The effects of agents that modulate intracellular release of calcium and protein kinase C (PKC) activation on noradrenaline (NA)-induced contractions of epididymal vas deferens in calcium-free/EGTA (1 mM) medium were investigated. NA (100 microM) or methoxamine (100 microM) evoked repeatable contractions. Clonidine (100-300 microM) was ineffective. The contractions to NA were reduced by procaine (1-10 mM) but not by thapsigargin (0.1-30 microM), ryanodine (1-30 microM) or TMB-8 (1-30 microM). Contractions to cumulative additions of NA (1-100 microM) were enhanced in the presence of cyclopiazonic acid (10 & 30 microM) but not ryanodine (10 & 30 microM). Sequential contractions to NA were not blocked by PKC inhibitors, calphostin C (1 microM) or Ro 31-8220 (1-30 microM) but were reduced by H-7 (1-30 microM), a broad spectrum protein kinase inhibitor. Although RT-PCR experiments detected mRNA for some Ca2+-dependent/DAG-activated and Ca2+-independent/DAG-activated PKC isoforms in epididymal vas deferens, the PKC activators, phorbol 12, 13-dibutyrate (100 microM) or phorbol 12-myristate 13-acetate (100 microM) failed to activate the tissues in calcium-free medium but enhanced subsequent contractions to NA. These results indicate a limited role for intracellular calcium stores and phorbol ester/DAG-sensitive PKC isoforms in NA-induced contraction of epididymal rat vas deferens in calcium-free medium. The results suggest that pharmacomechanical coupling triggered by NA may involve the sensitization of contractile myofilaments to Ca2+ or a Ca2+-independent mechanism. The possible involvement of Ca2+-independent/DAG-insensitive PKC isoforms and agonist-dependent but PKC-independent sensitization pathway is discussed.
Amobi
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Physiology Division, King's College London, Great Britain, UK.
Sugden
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Smith
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D000818:Animals; D002118:Calcium / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014649:Vas Deferens / Q000502:physiology*
D004791:Enzyme Inhibitors; D010703:Phorbol Esters; D012433:Ryanodine; D019284:Thapsigargin; D011493:Protein Kinase C; D002118:Calcium; D009638:Norepinephrine