Antonio Scarpa

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Values for ionized [Ca] in squid axons were obtained by measuring the light emission from a 0.1-mul drop of aequorin confined to a plastic dialysis tube of 140-mum diameter located axially. Ionized Ca had a mean value of 20 x 10(-9) M as judged by the subsequent introduction of CaEGTA/EGTA buffer (ratio ca. 0.1) into the axoplasm, and light measurement on a(More)
Inactivation of a dihydropyridine-sensitive calcium current was studied in a cell line (A7r5) derived from smooth muscle of the rat thoracic aorta. Inactivation is faster with extracellular Ca2+ than with Ba2+. In Ba2+, inactivation increases monotonically with depolarization. In Ca2+, inactivation is related to the amount of inward current, so that little(More)
Changes in ionized calcium were studied in axons isolated from living squid by measuring absorbance of the Ca binding dye Arsenazo III using multiwavelength differential absorption spectroscopy. Absorption changes measured in situ were calibrated in vitro with media of ionic composition similar to axoplasm containing CaEGTA buffers. Calcium loads of(More)
The passive ion permeability, regulation of volume, and internal pH of isolated bovine chromaffin granules were studied by radiochemical, potentiometric, gravimetric, and spectrophotometric techniques. Chromaffin granules behave as perfect osmometers between 340 and 1,000 mosM in choline chloride, NaCl, and KCl as measured by changes in absorbance at 430 nm(More)
Continuous nondestructive monitoring of intracellular ionized calcium in isolated squid axons by differential absorption spectroscopy (using arsenazo III and antipyrylazo III) was used to study uptake of calcium by carbonyl cyanide, p-trifluoromethoxy-phenylhydrazone (FCCP)- and (or) cyanide (CN)-sensitive and insensitive constituents of axoplasm. Known(More)
Patch clamp experiments were used to characterize the effect of dexamethasone on calcium currents in A7r5 cells. Pretreatment for 48 h with 200 nM dexamethasone did not affect the single channel conductance, the voltage dependence of channel opening, or the voltage-dependent inactivation of L-type channels. However, dexamethasone caused an approximately(More)
The chromaffin granule ATPase mediates an inwardly directed transport of H+ against concentration gradients, thereby forming and maintaining an electrochemical transmembrane H+ gradient. The kinetics of this ATPase, its activity modulation by changes in electrochemical H+ gradients, and the stoichiometry between H+ transport and ATP hydrolysis were studied(More)
The electrical potential (delta psi) and proton gradient (alpha pH) across the membranes of isolated bovine chromaffin granules and ghosts were simultaneously and quantitatively measured by using the membrane-permeable dyes 3,3'dipropyl-2,2'thiadicarbocyanine (diS-C3-(5)) to measure delta psi and 9-aminoacridine or atebrin to measure delta pH. Increases or(More)
Ca2+ entry under resting conditions may be important for contraction of vascular smooth muscle, but little is known about the mechanisms involved. Ca2+ leakage was studied in the A7r5 smooth muscle-derived cell line by patch-clamp techniques. Two channels that could mediate calcium influx at resting membrane potentials were characterized. In 110 mM Ba2+,(More)
ATP transiently increases the intracellular Ca2+ concentration in cardiac myocyte suspensions. Pretreatment with norepinephrine (NE) greatly potentiates the ATP response. We performed experiments on adult rat myocyte suspensions loaded with fura-2 to investigate the mechanism of NE potentiation. We found that forskolin (an activator of adenylate cyclase),(More)