Kinetics of Ca2+ release evoked by photolysis of caged InsP3 in rat submandibular cells

✍ Scribed by T. Takeo; S. Suga; J. Wu; Y. Dobashi; T. Kanno; M. Wakui

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 296 KB
• Volume: 174
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/(sici)1097-4652(199803)174:3<387::aid-jcp13>3.0.co;2-6

✦ Synopsis

Quantitative time-resolved measurements of cytosolic Ca 2/ release by photolysis of caged InsP 3 have been made in single rat submandibular cells using patch clamp whole-cell recording to measure the Ca 2/ -activated Cl 0 and K / currents. Photolytic release of InsP 3 from caged InsP 3 at 100 Joules caused transient inward (V H Å 60 mV) and outward (V H Å 0 mV) currents, which were nearly symmetric in their time course. The inward current was reduced when pipette Cl 0 concentration was decreased, and the outward current was suppressed by K / channel blockers, indicating that they were carried by Cl 0 and K / , respectively. Intracellular pre-loading of the InsP 3 receptor antagonist heparin or the Ca 2/ chelator EGTA clearly prevented both inward and outward currents, indicating that activation of Ca 2/ -dependent Cl 0 and K / currents underlies the inward and the outward currents. At low flash intensities, InsP 3 caused Ca 2/ release which normally activated the K / and Cl 0 currents in a mono-transient manner. At higher intensities, however, InsP 3 induced an additional delayed outward K / current (I K(delay) ). I K(delay) was independent of the initial K / current, independent of extracellular Ca 2/ , inhibited by TEA, and gradually prolongated by repeated flashes. The photolytic release of Ca 2/ from caged Ca 2/ did not mimic the I K(delay) . It is suggested that Ca 2/ releases from the InsP 3 -sensitive pools in an InsP 3 concentration-dependent manner. Low concentrations of InsP 3 induce the transient Ca 2/ -dependent Cl 0 and K / currents, which reflects the local Ca 2/ release, whereas high concentrations of InsP 3 induce a delayed Ca 2/ -dependent K / current, which may reflect the Ca 2/ wave propagation.