Isoprenaline reverses the slow force responses to a length change in isolated rabbit papillary muscle.
An alteration in the length of isolated cardiac muscle produces an immediate change in twitch force, then a slow further change in the same direction. We have found that the slow changes in force in rabbit papillary muscles are blocked or reversed by the beta-agonist, isoprenaline (1 microM). The abolition of the slow responses by isoprenaline was not due to saturation of the myofibrils with Ca2+, as the blockade continued if the extracellular [Ca2+] was reduced in the presence of isoprenaline so that twitch force was < 50% maximal. Ryanodine (1 microM) did not block the slow responses, suggesting that the sarcoplasmic reticulum does not mediate the responses. These results suggest that changes of intracellular [cAMP] may mediate, or at least modulate, the slow force responses to a length change in cardiac muscle.
Kentish
J C
JC
Department of Pharmacology, U.M.D.S., St. Thomas's Hospital, London, UK.
Davey
R
R
Largen
P
P
D000818:Animals; D000242:Cyclic AMP / Q000502:physiology; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D009210:Myofibrils / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology
D012433:Ryanodine; D000242:Cyclic AMP; D007545:Isoproterenol