The role of desensitisation in decay time of miniature endplate currents in frogs Rana ridibunda and Rana temporaria.
A new comparative characteristic of endplate microphysiology has been introduced. It is the feasibility of receptors to become desensitised as demonstrated on two frog species, Rana temporaria and Rana ridibunda: the decay times (tau(MEPC)) of single quantum miniature endplate currents (MEPCs) in the sartorius muscles of both species were about 1 ms and were not affected by the desensitisation-promoting agent proadifen when AChE was active. However, when the desensitisation was induced by anticholinesterase neostigmine and promoted by proadifen, the prolongation of tau(MEPC) from 1 ms was almost twice as great in Rana temporaria (tau(MEPC) = 4.4 ms) than in Rana ridibunda (tau(MEPC) = 3.1). This indicates that desensitisation reduces the number of available receptors and lowers the number of available ACh molecules for repetitive binding by trapping them by desensitised, high-affinity receptors significantly more in Rana ridibunda than in Rana temporaria. The application of proadifen, a promoter of desensitisation, decreased the prolongation of MEPCs in both species, but this shortening was more rapid in Rana ridibunda than in Rana temporaria. It is concluded that the desensitisation-induced reduction in the density, and the number of postsynaptic receptors is significantly higher at Rana ridibunda than in Rana temporaria endplates.
Giniatullin
R A
RA
Department of Animal Physiology and Developmental Biology, Faculty of Sciences, Charles University, Prague, Czech Republic.
Talantova
M V
MV
Vyskocil
F
F
D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D009045:Motor Endplate / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009388:Neostigmine / Q000494:pharmacology*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D011335:Proadifen / Q000494:pharmacology*; D011895:Rana ridibunda; D011896:Rana temporaria; D011950:Receptors, Cholinergic / Q000187:drug effects* / Q000378:metabolism; D013045:Species Specificity
D002038:Bungarotoxins; D002800:Cholinesterase Inhibitors; D004791:Enzyme Inhibitors; D011950:Receptors, Cholinergic; D009388:Neostigmine; D011335:Proadifen