L-type Ca2+ channels select for Ca2+ over sodium Na+ by an affinity-based mechanism. The prevailing model of Ca2+ channel permeation describes a multi-ion pore that requires pore occupancy by at least two Ca2+ ions to generate a Ca2+ current. At [Ca2+] < 1 microM, Ca2+ channels conduct Na+. Due to the high affinity of the intrapore binding sites for Ca2+ relative to Na+, addition of microM conc...

Na+/Ca2+exchange has been investigated in squid ( Loligo pealei) rhabdomeric membranes. Ca2+-containing vesicles have been prepared from purified rhabdomeric membranes by extrusion through polycarbonate filters of 1-μm pore size. After removal of external Ca2+, up to 90% of the entrapped Ca2+ could be specifically released by the addition of Na+; this finding indicates that most of the vesicles...

Coupled Na+ exit/Ca2+ entry (Na/Ca exchange operating in the Ca2+ influx mode) was studied in giant barnacle muscle cells by measuring 22Na+ efflux and 45Ca2+ influx in internally perfused, ATP-fueled cells in which the Na+ pump was poisoned by 0.1 mM ouabain. Internal free Ca2+, [Ca2+]i, was controlled with a Ca-EGTA buffering system containing 8 mM EGTA and varying amounts of Ca2+. Ca2+ seque...

Regulation of cytosolic Ca2+ and cytosolic Na+ is critical for lymphocyte cation homeostasis and function. To examine the influence of cytosolic Na+ on Ca2+ regulation in human peripheral blood lymphocytes, Ca2+ entry and cytosolic Ca2+ (measured with fura-2) were monitored in cells in which cytosolic Na+ was increased and/or the Na+ gradient was decreased by reduction of external Na+ concentra...

A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in pulmonary artery smooth muscle cells (PASMC) is an important stimulus for cell contraction, migration, and proliferation. Depletion of intracellular Ca2+ stores opens store-operated Ca2+ channels (SOC) and causes Ca2+ entry. Transient receptor potential (TRP) cation channels that are permeable to Na+ and Ca2+ are believed to form functional ...

Removing extracellular Na+ (Na+o) evoked a large increase in cytosolic free Ca2+ concentration ([Ca2+]i in human skin fibroblasts. Decreasing [Na+]o from 120 to 14 mM caused the half-maximal peak increase in [Ca2+]i. Removing Na+o strongly stimulated 45Ca2+ efflux and decreased total cell Ca2+ by about 40%. Bradykinin caused changes in [Ca2+]i, total Ca2+, and 45Ca2+ fluxes similar to those evo...

Bovine chromaffin-granule ghosts accumulate 45Ca2+ in a temperature- and osmotic-shock-sensitive process; the uptake is saturable, with Km 38 microM and Vmax. 28 nmol/min per mg at 37 degrees C. Entry occurs by exchange with Ca2+ bound to the inner surface of the membrane. It is inhibited non-competitively by Na+, La3+ and Ruthenium Red (Ki 10.7 mM, 7 microM and 2 microM respectively), and comp...

Although inhibition of the Na+/Ca2+ exchanger normally increases [Ca2+]i in neonatal cardiac myocytes, application of the inhibitor Ni2+ appears to reduce [Ca2+] measured by fluo-3. To investigate how the apparent reduction in [Ca2+]i occurs we examined Ca2+ transport by the human Na+/Ca2+ exchanger expressed in Sf9 cells. Transport of Ca2+ by the Na+/Ca2+ exchanger was examined using a laser-s...

Ca2+ signals in cardiac muscle cells are composed of spatially limited elementary events termed Ca2+ sparks. Several studies have also indicated that Ca2+ signals smaller than Ca2+ sparks can be elicited. These signals have been termed Ca2+ quarks and were proposed to result from the opening of a single Ca2+ release channel of the sarcoplasmic reticulum. We used laser-scanning confocal microsco...

The myoplasmic free Ca2+concentration ([Ca2+]i) was measured in intact single fibers from mouse skeletal muscle with the fluorescent Ca2+ indicator indo 1. Some fibers were perfused in a solution in which the concentration of Na+ was reduced from 145.4 to 0.4 mM (low-Na+solution) in an attempt to activate reverse-mode Na+/Ca2+exchange (Ca2+ entry in exchange for Na+ leaving the cell). Under nor...