The effects of Agauria salicifolia leaf extract on calcium current and excitation-contraction coupling of isolated frog muscle cells.
The effects of the ethanolic extract of Agauria salicifolia (AS) previously tested on sodium currents of normal and TTX-treated voltage-clamped skeletal and cardiac muscle cells was investigated on mechanisms involved in the excitation-contraction coupling of the same biological preparations. AS (10(-6) g/l) prolonged the action potential duration whereas the associated contraction was depressed. This is not due to the blocking action of AS on the tubular sodium current since similar results were obtained in the presence of high tetrodotoxin (TTX) concentrations. This is not due to some blocking action of AS on the L-type calcium current since this type of calcium current was enhanced by the extract. In contrast, the cardiac T-type calcium current was decreased by 10(-6) g/l AS. AS exerted a dose-dependent (tested for concentrations ranging from 5 x 10(-10) to 5 x 10(-5) g/l) inhibition of the two components of the contractile response elicited by durable depolarizations, with a prominent effect on the tonic phase. This effect was partially relieved by increasing the external divalent cation (Ca2+ or Cd2+) concentration. At the same concentration it shifted the inactivation/potential relationship for tension by 20 mV towards negative potentials. It is concluded that the inhibitory action of AS on excitation-contraction coupling is partly or completely due to the enhancement of the voltage- and Ca(2+)-dependent inactivation processes of the voltage-sensor.
Ecole Normale Supérieure, University of Yaoundé, Cameroon.
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G
Ewane-Nyambi
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P
Bois
G
G
Raymond
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D002413:Cations, Divalent / Q000494:pharmacology; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009132:Muscles / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010936:Plant Extracts / Q000494:pharmacology*; D010946:Plants, Medicinal; D011895:Rana ridibunda; D012508:Sarcolemma / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D002413:Cations, Divalent; D010936:Plant Extracts