This study employs the Patch Clamp technique to assess the function of two glucose sensitive potassium (K) channels in pancreatic B-cells in normal and diabetic (C57BL/KsJ-db) mice. Of these two channels one is blocked by membrane hyperpolarization and reduction of intracellular calcium, the other by increasing intracellular ATP. Both are believed to be important in the regulation of glucose induced insulin secretion. Insulin secretion studies have demonstrated that glucose-induced insulin release from the isolated pancreas of the db/db mouse appears to be normal at 7 weeks of age but is almost absent by 17 weeks. The animal is hyperinsulinemic at 7 weeks and insulinopenic at 17 weeks. The observation of an altered B-cell membrane potential electrical response to glucose in the later, insulinopenic, phase of the diabetes syndrome in the db/db mouse led us to hypothesize that the loss of glucose sensitivity of insulin secretion results form defective control of membrane K permeability. Experiments will be performed to locate the underlying cause of the altered electrical response in the insulinopenic db/db mouse B-cell. Studies of whole cell K current will identify the aberrant channel species; further experiments using cell attached and cell free patches as well as whole cell current studies will determine whether the altered control of K permeability involves alterations in channel conductance or sensitivity to intracellular second messengers, altered levels of intracellular second messengers or intracellular channel blocking ions, altered responses to physiological stimuli or alterations in the number of functional channels in the cell membrane. Completion of this section of the study is anticipated to require the three years for which funding is sought in this application. The following included to indicate the direction in which future research effort will be oriented. We further hypothesize that the loss of control of K permeability results form chronic stimulation of the B-cell from one or more of the external modulators of B-cell function and future studies will endeavor to identify the cause of the loss of glucose sensitivity of the older diabetic B-cell. To pursue this goal K channel function will be investigated in the normal mouse B-cell following culture under conditions which provoke hypersecretion, and which occur in the diabetic mouse, (hyperglycemia, hyperglucagonemia, hypercortisolism or vagal nerve hyperactivity (high levels of acetylcholine). This will determine whether the response of the normal B-cell can be modified to that of the diabetic B-cell. This, and the final series of experiments in which K channel behavior of B-cells from 7 week old diabetic mice will be assessed following exposure to the same treatments, will determine whether alteration of function in the db/db B- cell is in response to external stimuli alone or whether the db/db B-cell possesses an intrinsic defect which predisposes it to loss of function following chronic secretory stimulation.
| Ribalet, B; Eddlestone, G T (1995) Characterization of the G protein coupling of SRIF and beta-adrenergic receptors to the maxi KCa channel in insulin-secreting cells. J Membr Biol 148:111-25 |
| Ribalet, B; Eddlestone, G T (1995) Characterization of the G protein coupling of a somatostatin receptor to the K+ATP channel in insulin-secreting mammalian HIT and RIN cell lines. J Physiol 485 ( Pt 1):73-86 |
| Eddlestone, G T; Komatsu, M; Shen, L et al. (1995) Mastoparan increases the intracellular free calcium concentration in two insulin-secreting cell lines by inhibition of ATP-sensitive potassium channels. Mol Pharmacol 47:787-97 |
