The small GTPase Rem is a potent negative regulator of high voltage-activated Ca 2؉ channels and a known interacting partner for Ca 2؉ channel accessory ␤ subunits. The mechanism for Rem-mediated channel inhibition remains controversial, although it has been proposed that Ca V ␤ association is required. Previous work has shown that a C-terminal truncation of Rem (Rem-(1-265)) displays reduced in vivo binding to membranelocalized ␤2a and lacks channel regulatory function. In this paper, we describe a role for the Rem C terminus in plasma membrane localization through association with phosphatidylinositol lipids. Moreover, Rem-(1-265) can associate with ␤2a in vitro and ␤1b in vivo, suggesting that the C terminus does not directly participate in Ca V ␤ association. Despite demonstrated ␤1b binding, Rem-(1-265) was not capable of regulating a Ca V 1.2-␤1b channel complex, indicating that ␤ subunit binding is not sufficient for channel regulation. However, fusion of the CAAX domain from K-Ras4B or H-Ras to the Rem-(1-265) C terminus restored membrane localization and Ca 2؉ channel regulation, suggesting that ␤ binding and membrane localization are independent events required for channel inhibition.High voltage-activated Ca 2ϩ channels (Ca V 1 and Ca V 2 families) transduce electrical activity into increased intracellular calcium that mediates a diverse array of essential cellular processes, including hormone secretion, neurotransmitter release, and excitation-contraction coupling in muscle systems (1). The cardiac L-type Ca 2ϩ channel is a multiprotein complex consisting of the pore-forming Ca V 1.2 ␣ subunit and auxiliary subunits, including Ca V ␤ and ␣ 2 -␦ subunits (1). The Ca V ␣ subunit determines the ion selectivity and single channel conductance of the mature channel, whereas co-expression of Ca V ␤ or ␣ 2 ␦ facilitates cell surface trafficking of the ␣ 1 subunit, increases Ca 2ϩ current amplitude, and alters channel gating properties (1, 2). Ca V ␤ subunits are encoded by four genes (␤1-␤4), each subject to complex splicing (3). Ca V ␤2a, a ␤ isoform found in the heart, is subject to post-translational palmitoylation, which directs plasma membrane localization, whereas other ␤ isoforms are predominantly localized to the cytosol when not bound to Ca V ␣ 1 (3).Recently, members of the RGK 3 family of Ras-related GTPases, including Rem (4), Rem2 (5), Rad (6), and Gem/Kir (7), have been identified as potent regulators of HVA Ca 2ϩ channel function (8 -10). Although all RGK GTPases associate with Ca V ␤ subunits and prevent de novo expression of L-type I Ca (8 -10), the mechanism of RGK protein-mediated Ca 2ϩ channel inhibition remains controversial. It was originally hypothesized that RGK protein binding blocked Ca V ␣1/␤ association, leading to a reduction of functional channels at the cell surface (8,(11)(12)(13)(14). However, a series of recent studies suggests instead that the majority of RGK proteins inhibit the activity of the preassembled channel complex at the plasma membrane (10, 15, 16), although Ca V...

Aims The prevalence of highly insulin resistant diabetes is increasing and treatment requires the use of very high doses of insulin. This study was performed to analyze efficacy and patient satisfaction with use of U-500 concentrated insulin. Methods The medical records of 40 patients using U-500 insulin for at least 3 months were reviewed. A quality of life questionnaire was administered 6 or more months after U-500 was initiated. Effects of U-500 use on HbA1c, weight, total daily insulin use, hypoglycemia, and patient satisfaction were measured. Results Patients had uncontrolled diabetes for 3 years prior to U-500 initiation despite insulin titration. Subjects required continued insulin titration to attain glycemic control even after U-500 initiation, but HbA1c decreased by 1.5% within three months. Subjects gained weight with insulin titration. Hypoglycemic symptoms increased early after transition to U-500 insulin, but patients reported fewer hypoglycemic episodes on the quality of life questionnaire. Patient satisfaction with diabetes care and control was significantly improved following transition to U-500 insulin. Conclusions Use of U-500 insulin assists with attaining glycemic control in highly insulin resistant subjects, but at the cost of weight gain and increased insulin doses. However, patient satisfaction is improved with U-500 insulin use.

The use of U-500 insulin in the management of highly insulin resistant diabetic patients is growing. There are a number of reports that have noted the effects of U-500 insulin using multiple daily injections or continuous subcutaneous insulin infusion on hemoglobin A(1c), weight, and total daily insulin dosage. The effect of U-500 insulin use on glycemic control, changes in body weight, total daily insulin dosage, incidence of hypoglycemia, and effect on lipid levels and blood pressure as well as patient satisfaction and quality of life will be reviewed. In addition, this article will delineate algorithms of U-500 use, compare multiple daily injections or continuous subcutaneous insulin infusion, and discuss U-500 insulin pharmacokinetics.

Previous short-term studies evaluating U-500 insulin have reported improvements in glycemic control but with significant weight gain. This study was performed to examine the glycemic durability of U-500 insulin in highly insulin resistant subjects, and to determine if weight gain was continuous with use. Patients using U-500 insulin provided consent for chart reviews for up to 3 years prior to and 3 years after use of U-500 insulin. Charts were reviewed for physical and metabolic data from 53 subjects using U-500 insulin of which 20 used U-500 insulin for 3 years. Use of U-500 insulin led to an approximate 1% decrease in HbA1c within 3–6 months of use which was sustained for up to 3 years. Patients required increased insulin doses (by ~80%) over the first 6–12 months with a corresponding weight gain (~10 lbs) and a spike in hypoglycemia symptoms, but then insulin doses and body weight, as well as glycemic control and hypoglycemic symptoms, stabilized over subsequent follow up. Use of U-500 insulin in a clinical diabetes practice leads to sustained improvements in glycemic control following a period of insulin titration and weight gain. Despite the weight gain, glycemic control was sustained for up to 3 years.