Submitted on May 30, 2008
Revised on October 8, 2008
Accepted on November 3, 2008
INHIBITION OF SERINE/THREONINE PHOSPHATASE ENHANCES INHIBITION OF SERINE/THREONINE PHOSPHATASE ENHANCES ARACHIDONIC ACID-INDUCED [Ca2+]i VIA PROTEIN KINASE A
Tomoyuki Saino1 and Eileen L. Watson2*
1 Iwate Medical University
2 University of Washington
* To whom correspondence should be addressed. E-mail: ewatson{at}u.washington.edu.
Arachidonic acid (AA) regulates [Ca2+]i in a variety of cell types including salivary cells. In the present study, the effects of serine/threonine phosphatases on AA-induced Ca2+ signaling in mouse parotid acini were determined. Mice were euthanized with CO2. Treatment of acini with the serine/threonine phosphatase inhibitor, calyculin A (CAL), blocked both thapsigargin (THAPS) and carbachol (CARB)-induced Ca2+ entry but resulted in an enhancement of AA-induced Ca2+ release and entry. Effects were mimicked by the PP1 inhibitor, tautomycin (TAUT), but inhibited by the PP2A inhibitor, okadaic acid (OK). The protein kinase A (PKA) inhibitor, PKI(14-22), significantly attenuated AA-induced enhancement of Ca2+ release and entry in the presence of calyculin A, whereas, it had no effect on calyculin A-induced inhibition of thapsigargin- induced Ca2+ responses. The ryanodine receptor (RyR) inhibitor, tetracaine, and StHt-31, a peptide known to competitively inhibit RII binding to protein kinase A anchoring protein (AKAP), abolished calyculin A enhancement of AA-induced Ca2+ release and entry. StHt-31 also abolished forskolin (FOR) potentiation of 4-chloro-3-ethylphenol (4-CEP) and AA on Ca2+release, but had no effect on 8-pMeOPT-2'-O-Me-cAMP (8-pMeOPT) potentiation of 4-CEP responses. Results suggest that inhibition of PP1 results in an enhancement of AA-induced [Ca2+]i via PKA, AKAP and RyRs.
