FIGURE 7.

Maximal CCK stimulation of rat pancreatic acini causes formation of distinct Munc18b-SNARE complexes that mediate apical exocytosis. Dispersed rat pancreatic acini were treated with control Krebs-Ringer buffer with HEPES (KRBH, 1 h) or 100 pm CCK (1 h). 1 mg of protein of acini lysates was immunoprecipitated (IP) with anti-syntaxin 2 (A) or anti-syntaxin 3 (B) antibodies as described under “Experimental Procedures” or with preimmune IgG as an additional control. The precipitated proteins were separated on 12–15% gradient SDS-PAGE and identified with the indicated antibodies. Total lysates (25 μg of protein) serving as input controls showed similar levels of SNARE and Munc18b proteins in the various treatments. These blots are representative of two independent experiments. CCK typically gives responses of variable latency; we used 1 h of stimulation to ensure maximal coordinated recruitment of these dispersed acini.