Estimated cumulative incidence probabilities.

<p>The curves represent the estimated probabilities of an exocytotic event before time <i>t</i> (the cumulative incidence) for a given granule in healthy (upper panel, full curves) or diabetic (lower panel, dashed curves) <i>β</i>-cells. The black curves are obtained from model-free, non-parametric Kaplan-Meier estimates, which, for comparison, are shown in both panels. Steps in these curves correspond to exocytotic events. For the frailty model we show the marginal estimate (blue), and the estimates conditional on the frailty, <i>Z</i> = <i>η</i> (IRP granules; red; scaled by <i>π</i>_<i>X</i>) or <i>Z</i> = 1 (non-IRP granules; green; scaled by 1 − <i>π</i>_<i>X</i>). The gray vertical lines indicate the K⁺ pulses.</p

Stimulation protocol and related model parameters.

<p>An indication of the high-concentration K⁺ pulses (1 s) interspersed by 9 seconds of rest. The parameters common to the two statistical models are indicated in black (for the pulses following the first pulse) and gray (for the rest intervals). The two models have different parameters for the first pulse. In the Poisson model (red), the baseline rate and effect of diabetes is allowed to be different during the first pulse compared to subseequent pulses (black). In the frailty model (blue), the baseline parameters are the same during all the pulses, but additional parameters (<i>η</i>, <i>π</i>₁, <i>π</i>₂) describing the frailty distribution are included. These additional parameters are not restricted to a certain time interval. See main text for detailed descriptions of the statistical models.</p

Estimated parameters using Poisson modeling.

<p>Estimated parameters using Poisson modeling.</p

Estimated parameters using frailty modeling.

<p>Estimated parameters using frailty modeling.</p

Pentobarbital (PB) enhances the GABA-activated single-channel current.

<p>Single-channel currents recorded from the same cell is shown in <b>A</b>, <b>B</b> and <b>C</b> (Vp = −70 mV) and the all-points histograms (20 s) include the corresponding current trace. The solid line shows the time when the extracellular solution containing drug was perfused through the recording chamber. 100 µM pentobarbital potentiated and 100 µM SR-95531 inhibited the GABA-activated currents.</p

Identification of cell-types in rat pancreatic islets.

<p><b>A</b>. Hormone gene expression in single cells. Every three lanes on the gel contain RT-PCR products amplified with insulin (I), glucagon (G) and somatostatin (S) primers: Ins (195 bp), Gcg2 (328 bp) and Sst2 (140 bp), respectively (from left to right). The cell-type was identified according to which product had been detected. Positive controls were purified rat islets RNA samples and the negative control was water. <b>B</b>. The pie diagram illustrates the proportion of different cell-types discriminated by single-cell RT-PCR. <b>C.</b> Cell capacitance of α-cells (n = 18) and β-cells (n = 12). *P<0.05.</p

Interstitial GABA activates single-channel currents in intact islets.

<p>Single-channel currents that were later inhibited by 100 µM SR-95531 were recorded in four different cells (<b>A</b>, <b>B</b>, <b>C</b> and <b>D</b>) in intact rat islets. <b>A.</b> A representative current trace (top trace, slow time scale, s) showing GABA-activated single-channel currents and inhibition by 100 µM SR-95531. The solid line shows the time when the extracellular solution containing SR-95531 was perfused through the recording chamber. The broken lines indicate from where in the recording the current trace on the faster time scale (ms) was obtained. The glucose concentration was 20 mM and the holding potential was −90 mV (<b>A</b>), −70 mV (<b>B–D</b>). The most prominent single-channel conductance in the cells in A<b>,</b> B<b>,</b> C and D were 65 pS, 24 pS, 40 pS and 105 pS, respectively. For all four cells, the currents were recorded in the whole-cell patch-clamp configuration from cells in intact islets and were activated by interstitial GABA and inhibited by application of SR-95531 (100 µM).</p

Gene expression of GABA_A receptor subunits in rat pancreatic islets.

<p>Seventeen GABA_A receptor subunits were detected with the most prominent expression level for α1, α2, α4, α6, β3, γ1, δ and ρ1, ρ2, ρ3 subunits. The data is the average expression in islets from 6 rats.</p

Primers used to amplify cDNAs of rat insulin (Ins), glucagon (Gcg-1, Gcg-2), somatostatin (Sst-1, Sst-2), GABA_A receptor subunits and the reference gene β-actin (ACTB).

<p>Primers used to amplify cDNAs of rat insulin (Ins), glucagon (Gcg-1, Gcg-2), somatostatin (Sst-1, Sst-2), GABA_A receptor subunits and the reference gene β-actin (ACTB).</p

Interstitial GABA activates tonic GABA_A receptor currents in rat pancreatic islets.

<p><b>A.</b> A representative trace showing GABA-activated tonic current, recorded from a cell in an intact rat islet (Vp = −90 mV). The current was activated by interstitial GABA and inhibited by application of SR-95531, causing a clear outward shift in the holding current (line 1 to line 2). <b>B</b>. Gaussian fits to all-points histogram derived from 20 s current recordings in (A) before (1) and after (2) application of SR-95531. SR-95531 insensitive current was subtracted for analysis. The difference between the peaks of the Gaussian fits denotes the mean tonic current (5.3 pA). <b>C.</b> Whole-cell current-voltage (IV) relationship of GABA-activated current in rat islet cells (n = 3). The current activated by the interstitial GABA (I – I_SR-95531 = I_GABA) is plotted. The IV relation shows outward rectification. <b>D.</b> A representative current showing GABA-activated tonic current (21 pA, Vp = −90 mV) that is significantly larger than the current shown in (A). <b>E</b>. Gaussian fits to all-points histogram derived from 20 s current recordings in (D) before (1) and after (2) application of SR-95531. SR-95331 insensitive current was subtracted for analysis. <b>F</b>. Whole-cell IV relationship of GABA-activated current in rat islet cells (n = 3). The IV relation shows outward rectification.</p