Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Na/Ca exchange in squid axon.
Until recently, intracellular free calcium has been amenable to measurement and investigation only in cells large enough to permit either microinjection of a suitable Ca sensor such as a aequorin or arsenazo III or insertion of a Ca-sensitive microelectrode. This constraint on cell size was removed by the development of the fluorescent Ca2+ -sensitive dye Quin-2 and its acetoxymethyl ester, which can be introduced into a wide range of cell types. A major requirement of any intracellular Ca2+ indicator is that it should not disturb intracellular Ca2+ homeostasis and Quin-2 is generally considered to be satisfactory in this respect. We now report that injection of Quin-2 into squid (Loligo forbesi) axons can almost completely abolish one component of Ca2+ entry--intracellular Na+ (Nai)-dependent Ca2+ inflow, which occurs via Na/Ca exchange. Mixtures of Ca and Quin-2 that buffer an ionized Ca2+ at close to physiological concentrations also block Nai-dependent Ca2+ influx but these same mixtures fail to block the extracellular Na+ (Na0)-dependent extrusion of Ca2+, showing that Quin-2 acts specifically on Ca2+ inflow.
Allen
T J
TJ
Baker
P F
PF
D000634:Aminoquinolines / Q000494:pharmacology*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D049832:Decapodiformes; D007473:Ion Channels; D008094:Lithium / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*
D000634:Aminoquinolines; D007473:Ion Channels; D009025:Morpholines; C008550:morpholinopropane sulfonic acid; D008094:Lithium; D012964:Sodium; C035739:Quin2; D002118:Calcium