OBJECTIVE Acidosis produces a negative inotropic effect on cardiac muscle against which catecholamines and phosphodiesterase III inhibitors have limited therapeutic effects. This study evaluated the effects of colforsin, which directly activates adenylate cyclase without β-adrenergic receptor activation, in isolated Langendorff rat hearts in a pH- and concentration-dependent manner. DESIGN Ex...

Small trabeculae of rabbit left atrium immersed in TKBa solution (Tyrode with 10 mM K+ and 1 mM Ba2+) were used to study frequency dependence of "membrane" slow response excitability at long cycle lengths (greater than 1 s). In TKBa, stimuli generate graded, low-amplitude (2-15 mV) subliminal responses of variable long duration (up to 450 ms). A full all-or-none slow response is generated when ...

Background: Tumor Necrosis Factor α (TNFα) upregulation during acute inflammatory response has been associated with numerous cardiac effects including modulating Connexin43 and vascular permeability. This may in turn alter cardiac gap junctional (GJ) coupling and extracellular volume (ephaptic coupling) respectively. We hypothesized that acute exposure to pathophysiological TNFα levels can modu...

It was hypothesized that the caffeine derivative paraxanthine results in subcontracture increases in intracellular calcium concentration ([Ca(2+)](i)) in resting skeletal muscle. Single fibers obtained from mouse flexor digitorum brevis were loaded with a fluorescent Ca(2+) indicator, indo 1-acetoxymethyl ester. After a stable baseline was recorded, the fiber was superfused with physiological s...

A new method was developed to automatically measure the thickness of a single ventricular myocyte of guinea-pig heart. A fine marker was attached on the cell's upper surface and changes in its vertical position were measured by focusing it under the microscope. When the osmolarity of the bath solution was varied, the cell thickness reached a new steady level without any obvious regulatory volum...

Hawke, Thomas J., D. G. Allen, and M. I. Lindinger. Paraxanthine, a caffeine metabolite, dose dependently increases [Ca]i in skeletal muscle. J Appl Physiol 89: 2312–2317, 2000.—It was hypothesized that the caffeine derivative paraxanthine results in subcontracture increases in intracellular calcium concentration ([Ca]i) in resting skeletal muscle. Single fibers obtained from mouse flexor digit...

The L-type calcium current (ICa-L) was studied in single ferret ventricular myocytes using whole-cell recording with single patch pipettes. Voltage-clamp experiments were performed at room temperature with internal and external Na(+)- and K(+)-free Tyrode solutions in order to isolate ICa-L. For depolarizing steps eliciting small ICa-L the decay of the current is best described by one exponenti...

Previous studies have reported on propagation of individual spikes in isolated segments of the pregnant uterus, but there is no information on patterns of spike propagation in the intact organ. There is also no information on propagation of myometrial burst. The aim of this study was to record, at high resolution, patterns of propagation of electrical activities in the pregnant uterus. Sixteen ...

Isolated longitudinal smooth muscle from guinea pig ileum exposed to a high potassium depolarizing medium exhibited a sustained increase in muscle tone and an increase in potassium efflux. When the concentration of calcium ion in the medium was elevated the increase in muscle tone was enhanced, but the change in potassium efflux was reduced slightly. Lowering the calcium concentration diminishe...

A segment of a bundle of canine Purkinje fibers was encased in agar made up in Tyrode solution containing elevated K (47 ITIM) to depress the excitability of the segment. At a degree of depression producing total block of conduction in each direction through the depressed segment, exciting both ends of the bundle yielded full excitatory responses in the center of the depressed area. These respo...