Cataract formation is prevented by administration of verapamil to diabetic rats

Oxidative Stress-Induced TRPV2 Expression Increase Is Involved in Diabetic Cataracts and Apoptosis of Lens Epithelial Cells in a High-Glucose Environment

Cataracts are a serious complication of diabetes. In long-term hyperglycemia, intracellular Ca²⁺ concentration ([Ca²⁺]_i) and reactive oxygen species (ROS) are increased. The apoptosis of lens epithelial cells plays a key role in the development of cataract. We investigated a potential role for transient receptor potential vanilloid 2 (TRPV2) in the development of diabetic cataracts. Immunohistochemical and Western blotting analyses showed that TRPV2 expression levels were significantly increased in the lens epithelial cells of patients with diabetic cataracts as compared with senile cataract, as well as in both a human lens epithelial cell line (HLEpiC) and primary rat lens epithelial cells (RLEpiCs) cultured under high-glucose conditions. The [Ca²⁺]_i increase evoked by a TRPV2 channel agonist was significantly enhanced in both HLEpiCs and RLEpiCs cultured in high-glucose media. This enhancement was blocked by the TRPV2 nonspecific inhibitor ruthenium red and by TRPV2-specific small interfering (si)RNA transfection. Culturing HLEpiCs or RLEpiCs for seven days in high glucose significantly increased apoptosis, which was inhibited by TRPV2-specific siRNA transfection. In addition, ROS inhibitor significantly suppressed the ROS-induced increase of TRPV2-mediated Ca²⁺ signal and apoptosis under high-glucose conditions. These findings suggest a mechanism underlying high-glucose–induced apoptosis of lens epithelial cells, and offer a potential target for developing new therapeutic options for diabetes-related cataracts.

Inhibition of thioredoxin-interacting protein and inflammasome assembly using verapamil mitigates diabetic retinopathy and pancreatic injury

It has been previously demonstrated by our group that genetic inhibition of thioredoxin-interacting-protein (TXNIP) preserved retinal neuronal function in chemically-induced retinopathy. Moreover, elevated intracellular levels of TXNIP and calcium ions play important roles in hyperglycemia-induced oxidative stress and inflammation. Current study aimed to appraise the potential therapeutic benefits of pharmacological inhibition of TXNIP using verapamil in diabetic retinopathy. Diabetic retinopathy was assessed in type-1 diabetes rat model induced by a single intravenous injection of streptozotocin (45 mg/kg), with or without daily treatment with verapamil (10 mg/kg, oral) for 4 months. Verapamil treatment commenced 48 h post-streptozotocin insult and continued for 16 weeks. Untreated diabetic rats exhibited higher expression of toll-like-receptor-4 (TLR4), TXNIP, nucleotide-binding domain-like receptor protein-3 (NLRP3), caspase-1, cytochrome-c, and ssDNA as assessed immunohistochemically in both retinal and pancreatic tissues 16 weeks post-diabetes induction. This was associated with a reduced thioredoxin reductase (Trx-R) activity, increased release of TNF-α and IL-1β into vitreous fluid along with retinal ganglion cell (RGC) loss, pancreatic islets shrinkage, and enhanced CD34 expression. The treatment with verapamil enhanced Trx-R activity, significantly inhibited TLR4 mediated NLRP3-inflammasome assembly with subsequent diminishing of inflammatory markers (TNF-α and IL-1β) release into the vitreous, suppression of pathological angiogenesis, and preservation of RGC count and pancreatic islets diameter. Current study showed that using the calcium channel blocker, verapamil, interferes with the pathogenesis of diabetic retinopathy and pancreatic islets damage at multiple levels mainly through the inhibition of TLR4, TXNIP and NLRP3-inflammasome, suggesting its promising role as an anti-diabetic and a neuroprotective agent.

L-type calcium channels play a critical role in maintaining lens transparency by regulating phosphorylation of aquaporin-0 and myosin light chain and expression of connexins

Homeostasis of intracellular calcium is crucial for lens cytoarchitecture and transparency, however, the identity of specific channel proteins regulating calcium influx within the lens is not completely understood. Here we examined the expression and distribution profiles of L-type calcium channels (LTCCs) and explored their role in morphological integrity and transparency of the mouse lens, using cDNA microarray, RT-PCR, immunoblot, pharmacological inhibitors and immunofluorescence analyses. The results revealed that Ca (V) 1.2 and 1.3 channels are expressed and distributed in both the epithelium and cortical fiber cells in mouse lens. Inhibition of LTCCs with felodipine or nifedipine induces progressive cortical cataract formation with time, in association with decreased lens weight in ex-vivo mouse lenses. Histological analyses of felodipine treated lenses revealed extensive disorganization and swelling of cortical fiber cells resembling the phenotype reported for altered aquaporin-0 activity without detectable cytotoxic effects. Analysis of both soluble and membrane rich fractions from felodipine treated lenses by SDS-PAGE in conjunction with mass spectrometry and immunoblot analyses revealed decreases in β-B1-crystallin, Hsp-90, spectrin and filensin. Significantly, loss of transparency in the felodipine treated lenses was preceded by an increase in aquaporin-0 serine-235 phosphorylation and levels of connexin-50, together with decreases in myosin light chain phosphorylation and the levels of 14-3-3ε, a phosphoprotein-binding regulatory protein. Felodipine treatment led to a significant increase in gene expression of connexin-50 and 46 in the mouse lens. Additionally, felodipine inhibition of LTCCs in primary cultures of mouse lens epithelial cells resulted in decreased intracellular calcium, and decreased actin stress fibers and myosin light chain phosphorylation, without detectable cytotoxic response. Taken together, these observations reveal a crucial role for LTCCs in regulation of expression, activity and stability of aquaporin-0, connexins, cytoskeletal proteins, and the mechanical properties of lens, all of which have a vital role in maintaining lens function and cytoarchitecture.

GP-1447, an inhibitor of aldose reductase, prevents the progression of diabetic cataract in rats

We examined the effects of GP-1447 (3-[(4,5,7-trifluorobenzothiazol-2-yl)methyl]-5-methylphenyl acetic acid) on existing cataracts and sorbitol content in the lens in rats with streptozotocin-induced diabetes. GP-1447 is an inhibitor of aldose reductase, which is the first enzyme in the polyol pathway. Cataracts in the central region of the lens were observed in 7 of 14 eyes (50%) by the fifth week after induction of diabetes, and development of mature cataracts was observed in most lenses by the ninth week. In diabetic rats that received GP-1447 treatment beginning in the fifth week after induction of diabetes, progression of cataracts was observed for 1 week after initiation of treatment. Thereafter, the severity of cataracts did not change substantially. Sorbitol levels in the lens peaked during the first week of diabetes, and this increase was maintained during the 9-week observation period. Elevated sorbitol levels in the lenses of diabetic rats gradually declined after GP-1447 treatment was started on the fifth week after induction of diabetes. Cataracts and sorbitol elevation were not observed in the lenses of controls or diabetic rats treated with GP-1447 immediately after induction of diabetes. These results suggest that the polyol pathway plays an important role in both the appearance and progression of cataracts in diabetic rats. Inhibition of aldose reductase could significantly prevent progression of existing cataracts.

Effect of nifedipine on severe experimental cataract in diabetic rats

We examined the effects of Ca(2+)-channel blockers on sugar cataract formation in streptozotocin (65 mg/kg, i.v.)-induced diabetic rats that were given 5% D-glucose as drinking water. The diabetic rats were treated with an L-type Ca(2+)-channel blocker, nifedipine or verapamil, for 9 weeks from the 3rd day of streptozotocin injection. Using the full lens images of the horizontal plane captured with the new digital camera system that we developed recently, the cataract formation was quantitatively assessed in parallel with the conventional scaling method. In the animal model of diabetes mellitus, the cataracts at the peripheral region of the lens were detected 2 weeks after induction of hyperglycemia and progressed depending on the length of the diabetic period. The majority of them developed mature cataracts after 9 weeks of hyperglycemia. Nifedipine slowed the progression rate of diabetic cataracts without affecting the period of time required for the onset of this disease, whereas verapamil had no significant inhibitory effect on the diabetic cataract. These findings suggest that nifedipine may be considered as a candidate drug to suppress the progression of diabetic cataracts.

Diabetes-induced decrease in rat brain microsomal Ca2+-ATPase activity

The Ca(2+)-ATPase activity of rat brain microsomes was studied in streptozotocin (STZ)-induced diabetes. Male rats, 200-250 g, were rendered diabetic by injection of STZ (45 mg kg(-1) body weight) via the teil vein. Brain tissues were collected at 1, 4 and 10 weeks after diabetes was induced for determination of Ca(2+)-ATPase activity, lipid peroxidation and tissue calcium levels. Diabetic rats had significantly elevated blood glucose levels compared to controls. Blood glucose levels were 92.92 +/- 1.22 mg dl(-1) (mean +/- SEM) for the control group, 362.50 +/- 9.61 mg dl(-1) at 1 week and >500 mg dl(-1) at 4, 8 and 10 weeks for the diabetics. Enzyme activities were significantly decreased at 1, 4, 8 and 10 weeks of diabetes relative to the control group (p < 0.001). Ca(2+)-ATPase activity was 0.084 +/- 0.008 U l(-1), 0.029 +/- 0.005 U l(-1), 0.029 +/- 0.006 U l(-1), 0.033 +/- 0.003 U l(-1) and 0.058 +/- 0.006 U l(-1) (mean +/- SEM) at control, 1, 4, 8 and 10 week of diabetes respectively. The change in calcium levels in diabetic rat brain at 8 and 10 weeks of diabetes was significantly higher than that of the control group (p < 0.05). On the other hand lipid peroxidation measured as TBARS (thiobarbituric acid reactive substances) was significantly higher at 8 and 10 weeks of diabetes (p < 0.05). The increase in lipid peroxidation observed in diabetic rat brain may be partly responsible for the decrease in calcium ATPase activity.

Codelivery of a tea extract prevents morbidity and mortality associated with oral vanadate therapy in streptozotocin-induced diabetic rats

Oral administration of vanadate has a strong hypoglycemic effect but results in toxic side effects like life-threatening diarrhea. Tea is known to have potent antidiarrhea effects. We investigated the potential of suspending the vanadate in a tea decoction to reduce the diarrheatic action of vanadate. A concentrated extract of Lichee black tea was, therefore, added to sodium orthovanadate. Streptozotocin (STZ)-induced diabetic rats were orally gavaged with vanadate suspended in water or in the tea decoction, or with the tea extract alone. Blood glucose levels were assessed daily over 11 weeks with levels greater than 10 mmol/L warranting therapeutic intervention. Both the vanadate/water and vanadate/tea solutions acutely reduced blood glucose. The tea extract alone had no effect. The majority of vanadate/water-treated rats developed diarrhea and mortality rates approached 40%. Vanadate/tea-treated diabetic rats experienced no diarrhea or mortality and liver and kidney analyses (plasma ALT and creatinine, blood urea nitrogen [BUN], and urine-specific gravity) were normal. Animals treated with vanadate/tea retained blood glucose levels less than 10 mmol/L for an average of 24 consecutive days without subsequent treatments. Cataract formation was completely prevented. The mechanism of action of vanadate may have involved beta-cell stimulation because vanadate/tea-treated diabetic rats exhibited normal plasma insulin levels. In summary, because of its long-lasting effects, oral administration, and lack of side effects, vanadate/tea represents a potentially important alternative therapy for an insulin-deficient diabetic state.

Inhibition of experimental diabetic cataract by topical administration of RS-verapamil hydrochloride

AIM

To investigate the efficacy of verapamil eye drops for inhibition of diabetic cataract in rats.

METHODS

Diabetes was induced in 69 male Sprague-Dawley rats by an intraperitoneal injection of streptozotocin (65 mg/kg body weight). One group (DV) of animals was treated by instillation of one drop of 0.2% RS-verapamil hydrochloride in both eyes three times daily for 8 weeks. The placebo treated group (D) received the vehicle solution only. After 8 weeks the lenses were removed, inspected, and photographed using bright and dark field illumination. The transmission of He-Ne laser light was measured in the optical axis of each lens in order to determine the turbidity coefficient (t) as a measure of central lens opacity. Following digital image analysis, the integrated density as a measure of central and mid-peripheral opacities was determined.

RESULTS

Lenses of both groups developed peripheral cortical opacities not affecting the optical axis. Advanced and paracentral cortical opacities were present in 10 (16.7%) of the placebo treated lenses (D) and two (3.8%) of the verapamil treated lenses (DV). Complete corticonuclear cataract developed in four (6.7%) of the lenses from group D but none of the lenses from group DV. The mean lens turbidity t was determined to be 0.019 (SEM 0.002) mm(-1) (n = 52) in the verapamil treated diabetic rats (DV) and 0.042 (0.008) mm(-1) (n = 60) in the placebo treated group (D). This difference was statistically significant (p = 0.0054). The mean integrated density was 274.91 (22.5) in group D (n = 60) and 196.28 (20.7) in group DV (n = 37). This difference was also significant (p = 0.0037).

CONCLUSION

Verapamil eye drops 0.2% administered three times daily are effective in inhibiting the progression of lens opacities in streptozotocin diabetic rats.

The effect of verapamil in the prevention of radiation-induced cataract

PURPOSE

Cataract is an unavoidable complication when radiation therapy includes the lens, even in small doses. Alterations in the ion content of the lens were considered to play an essential role in cataract formation. In this experimental study, the effect of verapamil on ion concentrations within the irradiated lenses was investigated in rats.

METHODS AND MATERIALS

Forty female Wistar albino rats, each weighing 180-250 g, were divided into three groups: (a) radiation treated (n = 10); (b) no treatment (n = 10); (c) or a combination of radiation and verapamil (n = 20). Both the radiation group and verapamil-treated group received 5 Gy radiation to the cranium in a single fraction, including the eyes, within the irradiation volume. All animals were sacrificed by bleeding, 7.5 weeks posttreatment. Calcium, sodium, and potassium levels were measured in blood and in lens homogenates. However, for technical reasons, magnesium levels could only be studied in lens homogenates.

RESULTS

Potassium and sodium concentrations in lens homogenates did not differ in the control and radiation groups, but both were significantly lower in the verapamil-treated group (p = 0.001, p = 0.009, respectively). Calcium levels were higher in the radiation group and lower in the verapamil-treated group compared to the controls (p < 0.0001); magnesium levels did not differ (p = 0.37).

CONCLUSION

Verapamil effectively decreased the lens calcium concentration, which is accepted as the key element in radiation cataractogenesis. It is therefore concluded that verapamil may reduce the risk of radiation-induced cataract formation.

Contribution of osmotic changes to disintegrative globulization of single cortical fibers isolated from rat lens

In this study the contribution of osmotic changes to disintegrative globulization of lens cortical fibers was examined. Single fiber cells were isolated by trypsinization of adult rat lens cortex, and morphological changes elicited by exposure to different external solutions were monitored optically. The survival of the fiber-shaped cells was analysed in accordance with the Weibull distribution. Changes in [Ca2+]i were measured using the fluorescent calcium-sensitive dye-Fluo-3. Exposure of isolated fiber cells to Ringer's solution (containing 2 mm Ca2+) led to an exponential increase in [Ca2+]i with a time constant of 10.2+/-0.8 min, and caused disintegrative globulization in 25+/-4 min (=Tg). The process of globulization as well as the rate of increase in [Ca2+]i was delayed by removing Cl- ions from the external media. Globulization was also delayed by adding 20% bovine serum albumin (Tg=107+/-3 min) or chloride channel inhibitors 5, nitro-2-(3-phenylpropylamino) benzoate (NPPB), dideoxyforskolin, niflumic acid, and tamoxifen. When the fiber cells were suspended in isotonic (280 mm sucrose) HEPES-sucrose (HS) or HEPES-EDTA-sucrose (HES) solution, no globulization was observed for an observation time of 120 min. However, exposure to hypotonic (180 mm) HES solution led to disintegration of fiber cells in 75+/-7 min. Disintegration of the fiber induced by hypotonic HES solution could be delayed by either 0. 05 mm leupeptin (Tg=97+/-6 min) or by pre-loading the fibers with BAPTA (Tg=100+/-4 min). Inhibition of membrane calcium transport by 0.5 mm La3+ had no effect on Tg in hypotonic HES. Addition of 2 mm Ca2+ to HES solution accelerated globulization, and Tg was 57+/-4, 69+/-5 and 102+/-6 min for hypo-, iso- and hyper- tonic solutions, respectively. Transient exposure to calcium also accelerated disintegrative globulization of fiber cells exposed subsequently to HES solution. These results suggest that in ionic media, part of the calcium influx in isolated fiber cells is mediated by the influx of chloride ions. In the absence of other ions, the fiber cells still accumulate calcium, although this calcium influx was independent of medium tonicity. Globulization-induced by hypotonic sucrose solution appears to be mediated by the activation of intracellular proteases and by cell swelling-induced release of calcium from internal stores. Such swelling-mediated disintegrative globulization of fiber cells may be of significance in understanding the cellular basis of diabetic cataracts.

Lens lipid peroxides and glutathione concentrations in diabetic cataract

This study aims to explore the role of reactive oxygen radicals in the genesis of diabetic cataract. Lipid peroxide (LPO) concentrations in senile (n = 30) and diabetic (n = 14) cataractous lenses, were determined as thiobarbituric acid-reactive substances (TBARS) by a method modified from Satoh and Yagi, and reduced glutathione (GSH) concentrations were measured according to Beutler. Lens LPO levels (mean, SD; nmol TBARS/g protein) were significantly higher in diabetics (107.54, 18.12) than senile cataractous subjects (53.54, 15.48) (P < 0.0001). Lens GSH levels (mean, SD; nmol/g protein) showed no significant difference between diabetics (4.29, 2.05) and senile cataractous subjects (4.68, 3.12). These results suggest that free radical damage is more effective in the genesis of diabetic cataract than in senile cataract.

Differential effects of chronic calcium channel blocker treatment on the inotropic response of diabetic rat myocardium to acute ethanol exposure

Cardiomyopathy is a consistent feature of diabetic myocardium as well as in prolonged alcohol consumption. Diabetes-induced myocardial dysfunction has been attributed, in part, to calcium overload within individual myocytes. The present study compares the effectiveness of the calcium channel blocker nifedipine (dihydropyridine-type) with verapamil (phenylalkylamine-type) in reversing myocardial dysfunction and diminishing the negative inotropic effect of ethanol on diabetic rat myocardium. Wistar rats were made diabetic with streptozotocin (55 mg/kg, i.v.) and isolated electrically stimulated papillary muscles were studied under isometric conditions in the absence and presence of clinically relevant concentrations of ethanol (80-240 mg/dl, i e., 17.4-52.1 mM). Subgroups of diabetic and normal animals received daily injections of verapamil or nifedipine 2 weeks after induction of diabetes for 8 weeks. Untreated diabetic animals exhibited hyperglycemia, hyperlipidemia, reduced growth, cardiomegaly, and hepatomegaly. Compared to verapamil chronic nifedipine treatment normalized or reversed the effects of diabetes on myocardial mechanical function. The negative inotropic effect of ethanol was attenuated only in muscles from verapamil-treated diabetic animals. Thus, chronic nifedipine treatment may be more effective than verapamil in reducing hyperglycemia, attenuating both cardiac and liver enlargement, and restoring myocardial mechanical function, in experimental diabetes. However, chronic verapamil therapy is more effective in diminishing the negative inotropic effect of ethanol on diabetic myocardium. These findings may have clinical significance among diabetic patients who consume alcoholic beverages while receiving long-term calcium blocker therapy.

Influence of calcium channel blocker treatment on the mechanical properties of diabetic rat myocardium

The objective of this investigation was to determine whether calcium channel blocker (CCB) treatment effectively restores normal baseline mechanical function in diabetic myocardium and to evaluate its effect on the interval-strength relationship. Wistar rats were made diabetic with streptozotocin (55 mg/kg, IV). Left-ventricular papillary muscles from normal and diabetic (10 weeks) rats were superfused with Tyrode's solution at 30 degrees C. A subgroup of diabetic and normal animals received daily injections of verapamil or nifedipine (10 mg/kg, IP; 8 weeks) to compare the effectiveness of a phenylalkylamine to a dihydropyridine in reversing diabetes-induced contractile dysfunction in vitro. Muscles were electrically stimulated at 0.5 Hz with suprathreshold stimuli, and the following parameters were measured: peak tension developed, time to-peak tension, time-to-90% relaxation, and the maximum velocities of tension development and decay. Experimental diabetes was characterized by: severe hyperglycemia, hepatomegaly, reduced body weight gain, cardiomegaly, and increased plasma phospholipid levels. In addition, baseline values of peak tension developed, time to-peak tension, and time-to-90% relaxation were significantly greater in muscles from diabetic animals. Chronic nifedipine treatment reduced hyperglycemia and plasma phospholipid levels, normalized body weight gain, and reduced both heart and liver sizes in diabetic animals. Nifedipine treatment completely reversed diabetes-induced prolongation in both time-to-peak tension and time-to-90% relaxation. In diabetic myocardium, a slightly positive component was present in the interval-strength relationship between 0.01 and 1 Hz, resulting in a rightward shift in the entire curve across a wide range of stimulation frequencies (0.01-5 Hz). This positive component was absent in muscles from diabetic animals treated with both CCBs, and verapamil produced a leftward shift in the frequency response curve. The results of this study suggest that chronic nifedipine treatment may be more effective than verapamil in restoring normal baseline myocardial mechanical function, reducing hyperglycemia and hyperlipidemia, as well as attenuating both cardiac and liver enlargement in experimental diabetes. In contrast, verapamil treatment tended to normalize more effectively the inotropic response to changes in stimulation frequency in diabetic myocardium.

The effects of calcium channel blockers, verapamil, nifedipine and diltiazem, on metabolic control in diabetic rats

The effects of calcium channel blockers (CCB)-verapamil, nifedipine, diltiazem on metabolic control in streptozotocin-induced long-term diabetes in rats were investigated. Diabetes mellitus was induced by single intravenous injection of streptozotocin (65 mg/kg body wt.). The animals were divided into five groups: a healthy control group, a diabetic group and three diabetic groups treated with one of the calcium channel blockers (verapamil, 25 mg/kg/day, nifedipine, 20 mg/kg/day, and diltiazem, 30 mg/kg/day, respectively). Body weight, glycemia, glycated hemoglobin and total serum protein levels of these animals were measured at the beginning and at the end (after 13 weeks) of the experiment. It was observed that diabetic animals who were not treated with CCB had lost weight at the end of the experiment (P < 0.01). The blood glucose and glycated hemoglobin levels were increased in the diabetic group in comparison to the healthy control group (P < 0.001). However, the calcium channel blockers seem to have beneficial effects on body weight, glycated hemoglobin and blood glucose levels.

Inhibition of polyol formation in rat lens by verapamil

Accumulation of sorbitol and xylitol in rat lenses incubated in medium-199 with and without verapamil has been studied. This antihypertensive drug, known to attenuate hypertension by its calcium channel blocking effect, is also known to inhibit cataract formation in diabetes. The present studies have demonstrated that verapamil's effect against cataract could also be partially related to its aldose reductase inhibitory activity, in addition to the Ca++ channel blocking activity. The accumulation of sorbitol in the lenses incubated with high glucose in the presence of 400 microM verapamil was only 2.3 mmoles/Kg wet weight against 11.3 mmoles/Kg in its absence. The level of xylitol attained in the presence of 10 mM xylose was 25.7 +/- 2.4 mmoles/Kg. It decreased to 4.8 +/- 1.2 mmoles/Kg in presence of 400 microM verapamil. Hence, verapamil is significantly effective in inhibiting lens aldose reductase dependent polyol synthesis, an action simultaneous with its effect on calcium penetration.

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.