Independent changes of intracellular calcium and pH in identified leech glial cells

✍ Scribed by Prof.; Dr. Joachim W. Deitmer; Hans-Peter Schneider; Thomas Munsch

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 764 KB
• Volume: 7
• Category: Article
• ISSN: 0894-1491
• DOI: 10.1002/glia.440070405

✦ Synopsis

Abstract

The intracellular Ca^2+^ (Ca^2+^~i~) and the intracellular pH (pH~i~) were measured in identified neuropile glial cells in the central nervous system of the leech Hirudo medicinalis, using the fluorescent dye fura‐2, and double‐barrelled, neutral carrier, pH‐sensitive microelectrodes. Different stimuli were used to elicit Ca^2+^~i~ and/or pH~i~ changes, such as application of ammonium, high external K^+^‐concentration, and low external pH. Ammonium (20 mM) and high external K^+^ (20 mM), which depolarized the glial membrane by 20–30 mV, evoked rapid and large rises of Ca^2+^~i~. In contrast to the Ca^2^~i~ changes, amplitude and direction of the pH~i~ changes were dependent on the presence of CO~2~/HCO~3~^−^ in the saline. The addition of CO~2~/HCO~3~^−^, and the subsequent reduction of external pH from 7.4 to 7.0, had no effect on Ca^2+^~i~, but caused significant changes of pH~i~. The results suggest that the ammonium‐ and K^+^‐induced Ca^2+^~i~ rises were due to the membrane depolarization leading to a Ca^2+^ influx through voltage‐gated Ca^2+^ channels in the glial membrane, while the pH~i~ changes resulted from movements of ammonia and from the activation or inhibition of the Na^+^‐HCO~3~^−^ cotransporter. This indicates that changes of intracellular Ca^2+^ and pH can occur independently of each other, suggesting that the homeostasis of these ions is not necessarily interrelated in these glial cells.