pH changes in frog rods upon manipulation of putative pH-regulating transport mechanisms.
Rod intracellular pH (pHi) in the intact frog retina was measured fluorometrically with the dye 2',7'-bis(2-carboxyethyl)-5(and-6)-carboxyfluorescein under treatments chosen to affect putative pH-regulating transport mechanisms in the plasma membrane. The purpose was to relate possible pHi changes to previously reported effects on photoresponses. In nominally bicarbonate-free Ringer, application of amiloride (1 mM) or substitution of 95 mM external Na+ by K+ or choline triggered monotonic but reversible acidifications, consistent with inhibition of Na+/H+ exchange. Bicarbonate-dependent mechanisms were characterized as follows: (1) Replacing half of a 12 mM phosphate buffer by bicarbonate caused a sustained rise of pHi. (2) Subsequent application of the anion transport inhibitor 4,4'-diisothiocyanatostilbene-2',2'-disulphonic acid (DIDS, 0.2 mM) set off a slow acidification. (3) Substitution of external Cl- by gluconate (95 mM) caused a rapid pHi rise both in normal Na+ and low-Na+ perfusion. (4) This effect was inhibited by DIDS. The results support a consistent explanation of parallel electrophysiological experiments on the assumption that intracellular acidifications reduce and alkalinizations (in a certain range) augment photoresponses. It is concluded that both Na+/H+ exchange and bicarbonate transport control rod pHi, modulating the light-sensitive current. Part of the bicarbonate transport is by Na(+)-independent HCO3-/Cl- exchange, but a further Na(+)-coupled bicarbonate import mechanism is implicated.
Kalamkarov
G
G
Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia.
Pogozheva
I
I
Shevchenko
T
T
Koskelainen
A
A
Hemila
S
S
Donner
K
K
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D010775:Photic Stimulation; D011896:Rana temporaria; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D001639:Bicarbonates; D002712:Chlorides; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid