Resistance arteries exist in a maintained contracted state from which they can dilate or constrict depending on need. In many cases, these arteries constrict to membrane depolarization and dilate to membrane hyperpolarization and Ca-channel blockers. We discuss recent information on the regulation of arterial smooth muscle voltage-dependent Ca channels by membrane potential and vasoconstrictors...

We have explored the processes regulating presynaptic calcium concentration ([Ca(2+)](i)) in the generation of post-tetanic potentiation (PTP) at crayfish neuromuscular junctions, using spectrophotometric dyes to measure changes in [Ca(2+)](i) and [Na(+)](i) and effects of inhibitors of Ca(2+)-transport processes. The mitochondrial Na(+)/Ca(2+) exchange inhibitor CGP 37157 was without effect, w...

Protein phosphatase 2A (PP2A) plays central roles in development, cell growth and transformation. Inactivation of the gene encoding the PP2A catalytic subunit Ca by gene targeting generates a lethal embryonic phenotype. No mesoderm is formed in Ca embryos. Here, we found that during normal early embryonic development Ca was predominantly present at the plasma membrane whereas the highly homolog...

1. The carnivorous ciliate Didinium nasutum discharged its extrusive organelles when a strong inward current was injected into the cell in the presence of external Ca ions. 2. In the absence of external Ca ions, the strong inward current produced fusion of the apex membrane of the proboscis. 3. External application of Ca ions after the fusion of the apex membrane produced discharge of the organ...

The C2A domain is one of two calcium ion (Ca(2+))- and membrane-binding domains within synaptotagmin I (Syt I), the identified Ca(2+) sensor for regulated exocytosis of neurotransmitter. We propose that the mechanistic basis for C2A's response to Ca(2+) and cellular function stems from marginal stability and ligand-induced redistributions of protein conformers. To test this hypothesis, we used ...

Isolated human red blood cell membrane fragments (RBCMF) were found to take up Ca(++) in the presence of ATP.(1) This ATP-dependent Ca(++) uptake by RBCMF appears to be the manifestation of an active Ca(++) transport mechanism in the red cell membrane reported previously (Schatzmann, 1966; Lee and Shin, 1969). The influences of altering experimental conditions on Ca(++)-stimulated Mg(++) ATPase...

Although Ca-signaling processes are thought to underlie many dendritic cell (DC) functions, the Ca entry pathways are unknown. Therefore, we investigated Ca-signaling in mouse myeloid DC using Ca imaging and electrophysiological techniques. Neither Ca currents nor changes in intracellular Ca were detected following membrane depolarization, ruling out the presence of functional voltage-dependent...

Ion channels in the plasma membrane of vascular muscle cells that form the walls of resistance arteries and arterioles play a central role in the regulation of vascular tone. Current evidence indicates that vascular smooth muscle cells express at least 4 different types of K(+) channels, 1 to 2 types of voltage-gated Ca(2+) channels, >/=2 types of Cl(-) channels, store-operated Ca(+) (SOC) chan...

Carbonic anhydrases (CAs) are ubiquitous enzymes important to many cell types throughout the body. They help determine levels of H(+) and HCO(-)(3) and thereby regulate intracellular and extracellular pH and volume. CA XIV, an extracellular membrane-bound CA, was recently shown to be present in brain and retina. Here, we analyze the subcellular distribution of CA XIV in retina by high-resolutio...

A method is described for the preparation of ;free' and ;synaptosomal' brain mitochondria from fractions of guinea-pig cerebral cortex respectively depleted and enriched in synaptosomes. Both preparations of mitochondria have a low membrane H(+) conductance, a high capacity to phosphorylate ADP, and a capacity to accumulate Ca(2+) at rates limited by the activity of the respiratory chain. Ca(2+...