ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Intracellular pH (pH i ) and intracellular Ca2+ ([Ca2+] i ) were determined inChironomus salivary gland cells under various conditions of induced uncoupling. pH i was measured with aThomas-type microelectrode, changes in [Ca2+] i and their spatial distribution inside the cell were determined with the aid of intracellularly injected aequorin and an image intensifier-TV system, and cell-to-cell coupling was measured electrically. Treatments with NaCN (5mm), DNP (1.2mm), or ionophore A23187 (2μm) caused fall in junctional conductance (uncoupling) that was correlated with [Ca2+] i elevation, as was shown before (Rose & Loewenstein, 1976,J. Membrane Biol. 28:87) but not with changes in pH i : during the uncoupling induced by CN, the pH i (normally ≈ 7.5) decreased at most by 0.2 units; during the uncoupling induced by the ionophore, pH i fell by 0.13 or rose by 0.3; and in any one of these three agents' uncouplings, the onset of uncoupling and recovery of coupling were out of phase with the changes in pH i . Intracellular injection of Ca-citrate or Ca-EGTA solutions buffered to pH 7.2 or 7.5 produced uncoupling with little or no pH i change when their free [Ca2+] i was 〉10−5 m. On the other hand, such a solution at pH 4, buffered to [Ca2+]〈10−6 m, lowered pH i to 6.8 but produced no uncoupling. Thus, a decrease in pH i is not necessary for uncoupling in any of these conditions. In fact, uncoupling ensued also during increase in pH i : exposure to NH4HCO3 or withdrawal of propionate following exposure to a propionate-containing medium caused pH i to rise to 8.74, accompanied by [Ca2+] i elevation and uncoupling at pH i 〉7.8. Cell acidification itself can cause elevation of [Ca2+] i : injection (iontophoresis) of H+ invariably caused [Ca2+] i elevation and uncoupling. These effects were produced also by an application of H+-transporting ionophore Nigericin at extracellular pH 6.5 which caused pH i to fall to 6.8. Exposure to 100% CO2 produced a fall in pH i , associated in 10 out of 25 cases with [Ca2+] i elevation and, invariably, with uncoupling. The absence of a demonstrable [Ca2+] i elevation in a proportion of these trials is attributable to depression in Ca2+-measuring sensitivity; inin vivo tests, detection sensitivity for [Ca2+] i by aequorin was found to be depressed by the CO2 treatment. Upon CO2 washout, pH i and coupling recovered, but onset of recoupling set in at pH i as low as 6.32–6.88, generally lower than at the pH i at which uncoupling had set in. Exposure to 5% CO2 lowered pH i on the average by 0.3 and depressed coupling (in initially poorly coupled cells). After CO2-washout, pH i and coupling recovered. During the recovery phase [Ca2+] i was elevated, an elevation associated with renewed uncoupling or decrease in rate of recoupling. The results are discussed in connection with possible regulatory mechanisms of junctional permeability.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01944230
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