Xenopus oocyte resting potential, muscarinic responses and the role of calcium and guanosine 3',5'‐cyclic monophosphate.
- 1 July 1984
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 352 (1), 551-574
- https://doi.org/10.1113/jphysiol.1984.sp015310
Abstract
Resting potential (r.p.) and muscarinic response mechanisms were studied in X. laevis oocytes using the voltage-clamp technique. Insertion of micro-electrodes into the oocyte produced a ''shunt'' membrane conductance which partially sealed after a few minutes. The oocyte resting potential (measured with a single intracellular electrode) ranged from -40 to -60 mV. Ouabain and low K+ solution depolarized both follicles and denuded oocytes. The electrogenic Na+-K+ pump was more active in the latter. In the presence of ouabain, the r.p. agreed with the constant field theory. .alpha. (PNa+/PK+) was 0.12 in follicles and 0.24 in denuded oocytes. .beta. (PCl-/PK+) was 0.4 in both. At [Na+]o lower than 70 mM, the r.p. deviated considerably from the constant field predictions. The relatively large value of .alpha. indicated the major role of Na+ in oocyte r.p. determination. The oocyte muscarinic response was separated into four distinct components: the fast depolarizing Cl- current, ''D1''; the slow depolarizing Cl- current, ''D2''; the slow hyperpolarizing K+ current, ''H''; and the large membrane Cl- current fluctuation, ''F''. The H response reversal potential showed a Nernst relationship to [K+] and was selectively blocked by intracellular injection of tetraethylammonium (TEA). The D1 and D2 reversal potential showed a Nernst relationship to [Cl-]. In Ca2+-deficient, EGTA[ethyleneglycoltetraacetic acid]-containing medium, D2 and F were abolished and D1 and H were reduced. Verapamil inhibited all responses. Increasing [Ca2+]o caused a significant increase in D1, D2 and F response amplitudes. Intracellular injection of 0.6-10 pmol cGMP induced a large outward K+ current, similar to the muscarinic H response.This publication has 57 references indexed in Scilit:
- Adenosine-induced slow ionic currents in the Xenopus oocyteNature, 1982
- pH changes associated with meiotic maturation in oocytes of Xenopus laevisDevelopmental Biology, 1981
- Types of muscarinic response in oocytesLife Sciences, 1980
- Synaptic Potentials in Sympathetic Ganglia: Are They Mediated by Cyclic Nucleotides?Science, 1978
- Regulation of the amphibian oocyte plasma membrane ion permeability by cytoplasmic factors during the first meiotic divisionDevelopmental Biology, 1977
- Free calcium in full grown Xenopus laevis oocyte following treatment with ionophore A 23187 or progesteroneMolecular and Cellular Endocrinology, 1977
- The lonic permeability of the Amphibian oocyte in the presence or absence of external calciumJournal of Experimental Zoology, 1973
- Amino acid pools in developing oocytes of Xenopus laevisDevelopmental Biology, 1972
- The Selective Inhibition of Delayed Potassium Currents in Nerve by Tetraethylammonium IonThe Journal of general physiology, 1967
- Electrical Characteristics and Activation Potential of Bufo EggsThe Journal of general physiology, 1959