Ryanoids change the permeability of potassium channels of locust (Schistocerca gregaria) muscle.
The plasma membrane of locust skeletal muscle contains two types of K+ channel; a maxi, Ca2+-activated 170 pS channel (BK channel) and an inward rectifier of 35 pS conductance (IK channel). The effects of ryanodine, 9,21-didehydroryanodine and 9,21-didehydroryanodol on these channels have been investigated. In the concentration domain 10(-9) M to 10(-5) M, ryanodine irreversibly induced a dose-dependent reduction of the reversal potential (Vrev) of the channel currents, measured under physiologically normal K+ and Na+ gradients, i.e. from approximately 60 mV in the absence of ryanodine to approximately 15 mV for 10(-5) M ryanodine. The alteration of K+ channel selectivity was Ca2+ independent. 9,21-Didehydroryanodine and 9,21-didehydroryanodol reduced Vrev, but only to approximately 35 mV during application of 10(-5) M of these compounds. 9,21-Didehydroryanodine also diminished the conductances of the locust K+ channels. The three ryanoids reduced Vrev of a Ca2+-activated, high-conductance channel in inside-out patches excised from mouse interosseal muscle, although the changes were in each case less pronounced than those for the locust K+ channels. Also, the action of 9,21-didehydroryanodine on mouse K+ (BK) channels was restricted to a shift of Vrev. For all three ryanoids, the IC50 coefficients (i.e. the concentration of toxin that gave a 50% reduction in Vrev) for the shifts in Vrev were similar for the locust and mouse muscle K+ channels.
Vais
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Department of Life Science, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
Rucareanu
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Usherwood
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PN
D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D006110:Grasshoppers; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D051379:Mice; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010539:Permeability; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D012433:Ryanodine / Q000031:analogs & derivatives* / Q000494:pharmacology
D001952:Bridged-Ring Compounds; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; C101534:9,21-didehydroryanodol; D012433:Ryanodine; C062838:9,21-didehydroryanodine; D002118:Calcium