title: Modulations of membrane potential oscillations with drive, calcium overload, ryanodine, and caffeine.
abstract: The objective of this study is to determine the conditions that generate overdrive excitation and overdrive suppression in canine cardiac Purkinje tissue superfused in vitro. Drive-induced (3 Hz) perturbations in the membrane potential of a calcium overloaded (induced by strophanthidin) Purkinje fiber (from a canine heart) were differently modulated by caffeine and ryanodine. Whereas the postdrive oscillations in the membrane potential Vos (single or multiple oscillations in the diastole of the action potential) and/or spontaneous rate (postdrive suppression or postdrive excitation [PDE]) depended on the concentration of strophanthidin (PDE occurred at 2.5 x 10(-7) M, and Vos were seen variably at several concentrations), caffeine (2-3 mM) in the presence of a lower concentration of strophanthidin (1.25 x 10(-7) M) induced PDE. At these lower concentrations, either drug administered alone only induced Vos. On the contrary, the characteristic effects of ryanodine (10(-8) M) in the presence of strophanthidin (2.5 x 10(-7) M) were either a consistent postdrive suppression immediately or the induction of a pronounced afterdepolarization ([AD] a depolarization following the repolarization of the action potential) whose amplitude decreased with time and suppression. At higher concentrations of ryanodine (10(-5) M-10(-6) M) in a calcium overloaded tissue (strophanthidin, 1.25 x 10(-7) M) overdrive induced a pronounced AD in most cases, with subsequent depolarization and cessation of activity in less than 20 minutes. Ryanodine alone caused suppression of postdrive diastolic potential at lower concentrations (10(-9) M-10(-8) M), a pronounced AD (amplitude diminished with later drives), and suppression at higher concentrations (10(-6) M-10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, Meharry Medical College, Nashville, Tennessee 37208.
authors.forename: M L
authors.initials: ML
authors.lastname: Bhattacharyya
authors.forename: S
authors.initials: S
authors.lastname: Sarker
authors.forename: K
authors.initials: K
authors.lastname: Seth
authors.forename: B
authors.initials: B
authors.lastname: Hughes
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013327:Strophanthidin / Q000494:pharmacology*
chemical_list: D012433:Ryanodine; D002110:Caffeine; D013327:Strophanthidin; D002118:Calcium