TABLE 1.

Effects of membrane-permeant analogues of cAMP on the interaction of glucose and GLP-1(7-37) to depolarize rat pancreatic β-cells

Treatment	Number of cells tested	mV Change in membrane potential (±s.e.m.)
10 mM glucose	10	12 ± 5
10 mM glucose	5	35 ± 10*
10 nM GLP-1(7-37)
10 mM glucose	5	8 ± 6
10 μM Rp-cAMPS
10 mM glucose	5	10 ± 7
10 nM GLP-1(7-37)
10 μM Rp-cAMPS
10 mM glucose	5	40 ± 12*
10 μM Sp-cAMPS

Sp- and Rp-cAMPS were obtained from BioLog Life Science Institute, La Jolla, CA and prepared as 1 mM stock solutions in distilled water. The analogues were then diluted to a final concentration of 10 μM in the standard extracellular recording solution described in Fig. 1. Relatively glucose-insensitive β-cells were initially identified by testing for their inability to generate a substantial depolarizing response to 10 mM glucose applied for 30 s. After allowing 5 min recovery, such cells were subsequently challenged with a 30 s application of test solutions containing the indicated concentrations of glucose, GLP-1(7-37), and Sp-cAMPS. For those experiments examining the action of Rp-cAMPS the cells were pretreated in 10 μM Rp-cAMPS for 30 min at 37 °C. The cells were then challenged with the indicated test solutions containing glucose, GLP-1(7-37), and Rp-cAMPS. Statistical significance was evaluated by Student's t-test.

^*A value that is significantly different (P ⩽ 0.05) from control (10 mM glucose alone).