The factors controlling desensitization to ATP stimulation were investigated in PC12 cells. Reducing the concentration of ATP to produce half maximal response reduced the degree to which cells desensitize to ATP. Increasing external Me concentration, which produced a comparable decrease in the secretory response of the cells, had no effect on the degree of desensitization. Neither did decreasing external Ca2+ concentration, which produced a similar decrease in secretory response. Desensitizing cells in 0.5 mM Ca2+ did not result in a corresponding decrease in response when cells were subsequently tested in 2.2 mM Ca2+. PC12 cells desensitized in 2.2 mM Ca2+ were found to show the same degree of desensitization when tested in 0.5 mM Ca2+. A similar pattern was found when desensitization to 30 and 300 uM ATP was examined. The role of the ATP receptor subtypes, P2x and P2y, was studied using the ATP agonists 2-MeS ATP and UTP, respectively. 60 uM 2-MeS ATP was found to cause desensitization to the same degree as 30 uM ATP. As with ATP, the initial response to 2-MeS ATP was found to be sensitive to changes in external Mg2+. Unlike ATP, the desensitization to 2-MeS ATP was sensitive to changes in external Mg2+. When cells were co-stimulated with 2-MeS ATP and UTP, the sensitivity of 2-MeS ATP desensitization to Mg2+ remained. UTP in the background solution, however, increased desensitization to ATP and 2-MeS ATP. The effect of voltage-operated Ca2+ channel (VOCC) blockers on the response and desensitization to ATP and 2-MeS ATP was examined. Cd2+ produced a significant increase in the secretory response to both stimulants. Both nicardipine and Cd2+ increased the rate of desensitization to ATP. Only nicardipine was able to increase the rate of desensitization to 2-MeS ATP. These results were integrated to provide insights into the relationship between ATP receptors and VOCCs.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-3420 |
| Date | 01 January 2000 |
| Creators | Keath, Jerry Russel |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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