Michael Berridge | PubMed Health

PubMed2004

Conformational coupling: a physiological calcium entry mechanism.

The entry of external Ca2+ that is activated by inositol 1,4,5-trisphosphate (IP3) may occur through a conformation coupling mechanism. IP3 receptors in the endoplasmic reticulum located in a junctional zone make contact with entry channels in the plasma membrane. IP3 may act directly to stimulate this coupling complex or IP3 could act indirectly by stimulating uncoupled IP3Rs in the vicinity of the junctional zone to induce a localized depletion of the ER store to switch on a store-operated mechanism. At physiological agonist concentrations, the earliest Ca2+ response to receptor activation may be the stimulation of entry, which is then responsible for charging up the internal store to prime the IP3Rs for the large-scale regenerative release of Ca2+ that occurs during each spike.

Animals↗

PubMed2004

Mitochondrial gene-knockout (rho0) cells: a versatile model for exploring the secrets of trans-plasma membrane electron transport.

Plasma membrane electron transport (tPMET) pathways have been identified in all living cells, and a wide variety of tools have been used to study these processes. In our laboratory we have used the cell-impermeable tetrazolium dye WST-1, together with the mitochondrial gene knockout (rho0) cell model, to investigate one of these pathways. We have shown that growth of HL60rho0 cells is dependent on oxygen, and that these cells consume oxygen at the cell surface. Similarities in inhibition profiles between non-mitochondrial oxygen consumption and WST-1 reduction suggest that both systems share a common tPMET pathway. In support of this, oxygen was shown to compete with the intermediate electron acceptor that mediates WST-1 reduction, for reducing electrons. The observation that tPMET activity is higher in rho0 cells compared to their mitochondrially-competent counterparts was shown to be the result of competition between the mitochondrial and plasma membrane electron transport systems for intracellular reducing equivalents. Elevated rates of dye reduction appear to be mediated through increased expression of the key components of tPMET, which include the cell surface NADH oxidase, CNOX. These findings have played a critical role in shaping our current understanding of the mechanisms of this particular pathway of tPMET.

Cell Line, Tumor↗