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Am J Physiol Cell Physiol 273: C1588-C1595, 1997;
0363-6143/97 $5.00
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Vol. 273, Issue 5, C1588-C1595, November 1997

Niflumic acid differentially modulates two types of skeletal ryanodine-sensitive Ca2+-release channels

Toshiharu Oba

Department of Physiology, Nagoya City University Medical School, Nagoya 467, Japan

The effects of niflumic acid on ryanodine receptors (RyRs) of frog skeletal muscle were studied by incorporating sarcoplasmic reticulum (SR) vesicles into planar lipid bilayers. Frog muscle had two distinct types of RyRs in the SR: one showed a bell-shaped channel activation curve against cytoplasmic Ca2+ or niflumic acid, and its mean open probability (Po) was increased by perchlorate at 20-30 mM (termed "alpha -like" RyR); the other showed a sigmoidal activation curve against Ca2+ or niflumic acid, with no effect on perchlorate (termed "beta -like" RyR). The unitary conductance and reversal potential of both channel types were unaffected after exposure to niflumic acid when clamped at 0 mV. When clamped at more positive potentials, the beta -like RyR channel rectified this, increasing the unitary current. Treatment with niflumic acid did not inhibit the response of both channels to Ca2+ release channel modulators such as caffeine, ryanodine, and ruthenium red. The different effects of niflumic acid on Po and the unitary current amplitude in both types of channels may be attributable to the lack or the presence of inactivation sites and/or distinct responses to agonists.

frog skeletal muscle sarcoplasmic reticulum; single-channel activity; activation and inactivation sites; perchlorate; ryanodine receptor agonists


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