Voltage- and time-dependent action of histrionicotoxin on the endplate current of the frog muscle
نویسندگان
چکیده
Histrionicotoxin, a toxin isolated from skin secretions of a Colombian arrow poison frog, Dendrobates histrionicus, decreased the amplitude and time-course of the endplate current, and altered the voltage dependence of the half-decay time. In addition, the toxin produced a characteristic nonlinearity in the current-voltage relationship of the endplate current when 3-s voltage conditioning steps were used. Reduction in time of the conditioning steps to 10 ms made the current-voltage relationship linear. The decrease in peak amplitude of the endplate current (epc) produced by histrionicotoxin measured during long hyperpolarizing conditioning steps was fitted by a single exponential function. The calculated rate constants ranged from 0.03 to 0.14 s-1 and varied with membrane potential at hyperpolarizing levels. The voltage- and time-dependent action of histrionicotoxin does not require an initial activation of receptors by acetylcholine (ACh). The characteristic of the current-voltage relationship can be accounted for by the observed voltage and time dependency of the attenuation of the endplate current amplitude in the presence of histrionicotoxin during long conditioning steps. These effects of histrionicotoxin on the peak amplitude, and on the voltage and time dependence of the epc were concentration-dependent and slowly reversible upon washing out the toxin. Thus, the voltage- and time-dependent action of histrionicotoxin at the endplate is related to an increase in the affinity between the toxin and the ACh receptor-ionic channel complex. This increase in affinity is postulated to be due to a conformational change of the macromolecule in the presence of histrionicotoxin which is demonstrated to be relatively slow, i.e., on the order of tens of seconds.
منابع مشابه
Voltage-dependence of drug-induced conductance in frog neuromuscular junction.
Membrane currents from voltage-clamped frog muscle fibers were recorded during iontophoretic application of steady doses of carbachol, acetylcholine, and suberyldicholine to the endplate region. In the presence of these drugs, an exponentially relaxing current was observed after step changes of membrane potential. The time constant of relaxation was found to be voltage-dependent. It was equal t...
متن کاملجریانهای یونی کانالهای پتاسیمی و کلسیمی در سلولهای ایزوله شده عضله صاف سمینال وزیکول خوکجه و مهاراین جریانها بوسیله Glibenclamide
Smooth muscle cells of seminal vesicle exhibit excitatcry junction patential on nerve stimulation and can fire evoked) action potential (1). However) the type of ion channels that underlie this electrical activity have not been described. I have investigated the type and pharmacology of ion channel in freshly isolated smooth muscle cells from the guinea-pig seminal vesicle using whole-cell patc...
متن کاملA Linear Dose-Response Curve at the Motor Endplate
The motor endplate of frog sartorius muscle was voltage clamped and the peak current to different concentrations of acetylcholine and carbachol applied in the perfusing fluid was measured. Perfusing fluid was hypertonic in order to suppress contractions. Current responses were smooth and reached a peak value within 2-5 s. The dose-response curve was usually linear even with concentrations of 10...
متن کاملBlock of endplate channels by permeant cations in frog skeletal muscle
Motor endplates of frog semitendinosus muscles were studied under voltage clamp. Current fluctuations induced by iontophoretic application of acetylcholine were analyzed to give the elementary conductance, gamma , and mean open time, tau , of endplate channels. Total replacement of the external Na+ ion by several other metal ions and by many permeant organic cations changed both gamma and tau ....
متن کاملThe effect of lead (Pb2+) on electrophysiological properties of calcium currents in F77 neuron in Helix aspersa
Ion channels are responsible for control of cell function in excitable tissues such as heart and brain and also in organs and tissues traditionally thought to be non- excitable including liver and epithelium. In the present research, the effect of lead (Pb2+) on Ca2+ -dependent action potential and currents was studied in F77 neuronal soma membrane of Helix aspersa. For this purpose, action pot...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- The Journal of General Physiology
دوره 72 شماره
صفحات -
تاریخ انتشار 1978