Effects of epinephrine on resting and tonic tensions of rat extraocular muscles.
"In vitro" epinephrine (10(-6) to 10(-4) M) stimulates the rat inferior rectus, one of the extraocular muscles (EOMs). When applied to resting muscles, it induces a slow rising tension in about one half of the preparations. The amplitude of this tension is equivalent to about 9% of the maximal tetanic response. This effect is blocked by propranolol (10(-7) to 10(-6) M). When epinephrine is applied prior to a depolarization of the muscle fibers with 30 mM K, the drug consistently induces a significant potentiation of the long lasting tonic tension normally evoked by that elevated K concentration. One possible explanation for these results is that epinephrine induces a slow rising tension by increasing a resting Ca conductance of the sarcolemma of the tonic or Felderstruktur fibers of EOM.
D000818:Animals; D004837:Epinephrine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009801:Oculomotor Muscles / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains
D004837:Epinephrine