Cav 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons

OBJECTIVE

An increase of neuronal Ca_v 1.3 L-type calcium channels (LTCCs) has been observed in various animal models of epilepsy. However, LTCC inhibitors failed in clinical trials of epileptic treatment. There is compelling evidence that paroxysmal depolarization shifts (PDSs) involve Ca²⁺ influx through LTCCs. PDSs represent a hallmark of epileptiform activity. In recent years, a probable epileptogenic role for PDSs has been proposed. However, the implication of the two neuronal LTCC isoforms, Ca_v 1.2 and Ca_v 1.3, in PDSs remained unknown. Moreover, Ca²⁺ -dependent nonspecific cation (CAN) channels have also been suspected to contribute to PDSs. Nevertheless, direct experimental support of an important role of CAN channel activation in PDS formation is still lacking.

METHODS

Primary neuronal networks derived from dissociated hippocampal neurons were generated from mice expressing a dihydropyridine-insensitive Ca_v 1.2 mutant (Ca_v 1.2DHP^-/- mice) or from Ca_v 1.3^-/- knockout mice. To investigate the role of Ca_v 1.2 and Ca_v 1.3, perforated patch-clamp recordings were made of epileptiform activity, which was elicited using either bicuculline or caffeine. LTCC activity was modulated using the dihydropyridines Bay K 8644 (agonist) and isradipine (antagonist).

RESULTS

Distinct PDS could be elicited upon LTCC potentiation in Ca_v 1.2DHP^-/- neurons but not in Ca_v 1.3^-/- neurons. In contrast, when bicuculline led to long-lasting, seizure-like discharge events rather than PDS, these were prolonged in Ca_v 1.3^-/- neurons but not in Ca_v 1.2DHP^-/- neurons. Because only the Ca_v 1.2 isoform is functionally coupled to CAN channels in primary hippocampal networks, PDS formation does not require CAN channel activity.

SIGNIFICANCE

Our data suggest that the LTCC requirement of PDS relates primarily to Ca_v 1.3 channels rather than to Ca_v 1.2 channels and CAN channels in hippocampal neurons. Hence, Ca_v 1.3 may represent a new therapeutic target for suppression of PDS development. The proposed epileptogenic role of PDSs may allow for a prophylactic rather than the unsuccessful seizure suppressing application of LTCC inhibitors.

Single high-dose peroral caffeine intake inhibits ultraviolet radiation-induced apoptosis in human lens epithelial cells in vitro

PURPOSE

The aim of the present study was to determine whether caffeine concentrations in human lens epithelial cells (LECs) achieved from acute peroral caffeine intake inhibit ultraviolet radiation-induced apoptosis in vitro.

METHODS

Patients were planned for cataract surgery of both eyes with a caffeine abstinence of 2 weeks in total, starting 1 week before surgery of the first eye. The second eye was scheduled 1 week after the first eye. At the day of the second eye surgery, patients were given coffee containing 180 mg caffeine shortly before surgery. Lens capsules including LEC, harvested after capsulorhexis, were transferred to a cell culture dish and immediately exposed to close to threshold ultraviolet radiation (UVR). At 24 hr after UVR exposure, apoptotic LECs were analysed by TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining.

RESULTS

TUNEL-positive cells were detected in UVR-exposed lens capsules both after caffeine intake and in controls. The mean difference in TUNEL-positive cells between caffeine intake and contralateral controls (no caffeine) resulted in a 95% CI 15.3 ± 10.4% (degrees of freedom: 16).

CONCLUSION

Peroral caffeine consumption significantly decreased UVR-induced apoptosis in LEC supporting epidemiological findings that caffeine delays the onset of cataract.