Do catecholamines directly modulate the delayed plateau potassium current in frog atrium?

An important electrophysiological action of catecholamines in the heart is the modulation of the second inward current (iCa). Catecholamine augmentation of iCa has been attributed to an increase in the number of functional channels, as well as an increase in the probability of channel opening [1, 4, 12]. Another important electrophysiological action of catecholamines in the heart is the modulation of time-dependent outward currents.

Comparative interactions of organic Ca++ channel antagonists with myocardial Ca++ and K+ channels.

Dose-dependent inhibition by three organic calcium channel antagonists, D-600, nisoldipine and diltiazem, of the inward calcium current (iCa) and the delayed, outward potassium current (iK) in single frog atrial cells was examined using a voltage clamp technique. At holding potentials of -60 mV, low concentrations of these antagonists produced considerable inhibition of iCa without significant alterations in iK, suggesting that iK in single frog atrial cells is not a calcium-activated K+ conductance. Higher concentrations of each of these antagonists, however, inhibited iK.

Interactions of organic calcium channel antagonists with calcium channels in single frog atrial cells.

Inhibition of whole-cell calcium currents in enzymatically dispersed frog atrial myocytes by D-600, diltiazem, and nifedipine was studied using a single-micropipette voltage-clamp technique. The objective of these experiments was to test the applicability of a modulated-receptor hypothesis similar to that proposed for local anesthetic interactions with sodium channels to account for the tonic and frequency-dependent interactions of these organic compounds with myocardial calcium channels. Data consistent with such a hypothesis include: (a) prominent use-dependent block of iCa by D-600 and diltiazem, which are predominantly charged at physiological pH; (b) iCa block by an externally applied, permanently charged dihydropyridine derivative is greatly attenuated; (c) all three antagonists produce large negative shifts in the voltage dependence of iCa availability; (d) block of iCa by these compounds is state-dependent; (e) reactivation of iCa in the presence of all three antagonists is biexponential, which suggests that drug-free channels recover with a normal time course and drug-bound channels recover more slowly; and (f) the kinetics of the drug-induced slow iCa recovery process may be determined largely by factors such as size and molecular weight, in addition to lipid solubility of the compounds.

Presynaptic and postsynaptic actions of cadmium in cardiac muscle.

A transmembrane flux of Ca2+ has been demonstrated in many nerve and muscle cells. In cardiac muscle, Ca2+ channels in the sarcolemma transfer sufficient Ca2+ to trigger and partially control tension development. This time- and voltage-dependent Ca2+ current is also important in the development of the pacemaker potential, or diastolic depolarization.

Ionic currents in single isolated bullfrog atrial cells.

Enzymatic dispersion has been used to yield single cells from segments of bullfrog atrium. Previous data (Hume and Giles, 1981) have shown that these individual cells are quiescent and have normal resting potentials and action potentials. The minimum DC space constant is approximately 920 microns.

Active and passive electrical properties of single bullfrog atrial cells.

Single cells from the bullfrog (Rana catesbeiana) atrium have been prepared by using a modification of the enzymatic dispersion procedure described by Bagby et al. (1971. Nature [Long.

Physiological role of endogenous amines in the modulation of ventricular automaticity in the guinea-pig.

1. Current-clamp experiments were carried out with guinea-pig papillary muscles to determine the dependence of depolarization-induced automaticity on endogenous catecholamines. 2.

Expected hemotherapy in elective surgery. A follow-up.

Preoperative cross match guidelines were developed from a review of elective surgical hemotherapy. Six elective surgical procedures were studied prospectively to determine the effectiveness of the recommendations. All six procedures demonstrated a substantial reduction in preoperative cross match ordering during the study period, although for only one procedure was the guidelines' recommendation followed strictly.

Sea-Level Changes during the Last 2000 Years at Point Barrow, Alaska.

Eustatic rises of sea level between A. D. 265 and 500 and between A.