Exp Eye Res. used to activate currents, as expected for slow inosine 5 triphosphate hydrolysis by G-proteins. Still, other results remain suggestive of regulatory roles for PIP2. First, the cGMP concentration producing half-maximal CNG channel activity (oocytes. These effects were evaluated in both homotetramers and in heterotetramers. In addition, we studied possible effects of PIP2generated in the oocyte patches in dependence on MgATP. After describing the effects of PIP2 and MgATP on expressed channels, we turn to effects of PIP2and MgATP in photoreceptor outer segments. Giant rod cell patches allow us to examine regulation of the phototransduction cascade while maintaining cytoplasmic access. Our results demonstrate remarkably efficient, membrane-tethered guanine nucleotide phosphorylation mechanisms in excised patches. Furthermore, BIBR 1532 our results suggest that phosphoinositides promote the activation of phosphodiesterase (PDE) by transducin, as well as modulate CNG channel activity. Our conclusions about PDE activation are supported by both electrophysiological and biochemical measurements. MATERIALS AND METHODS The cDNA clone of the subunits (Kaupp et al., 1989) was provided by W. N. Zagotta (University of Washington, Seattle, WA) and the cDNA clone of the subunits (Chen et al., 1993) was supplied by K. W. Yau (Johns Hopkins University, Baltimore, MD). The cDNAs were both in a pGMEHE vector supplied by E. R. Liman (University of Southern California, Los Angeles, CA). RNA was transcribed Rabbit Polyclonal to MMP-9 using the Mmessage Mmachine transcription kit (Ambion, Austin, TX) and was injected intooocytes, which were maintained at 14C for 3C10 d. All results presented from photoreceptor cells are patch-clamp records from rod cells. The frogs were commercially obtained and kept at room temperature with 12 hr light/dark cycles, except when the experiment required dark adaptation. The frogs were decapitated and double-pithed. The eyes were quickly removed, and the globe was sectioned in half and placed immediately in a modified frog Ringer’s solution at 4C, which consisted of NaCl 111 mm, KCl 2.5 mm, CaCl2 1 mm, HEPES 3 mm, MgCl2 1.2 mm, dextrose 10 mm, and EDTA 20 m, pH 7.6 withRecordings were made from excised, giant patches in the inside-out configuration as described previously (Hilgemann and Lu, 1998). Pipette tip diameters were 15C40 m BIBR 1532 for oocyte patches and were 5C7 m for rod cell patches. In the rod cell recordings, the diameter of the pipettes was large enough, relative to the diameter of the rod cells, so that the cells generally doubled over and were squeezed into the pipette tip by 5C10 m before the gigaohm seal formed. The two protruding ends of the rod cell were then broken off with a solution stream from a polyethylene tube pointed at the patch tip. This technique allowed retention of 3C50% of the cell in the patch. Most recordings were made at a holding potential of 0 mV using a pipette solution containing (in mm) KCl 20, HEPES 10, CaCl2 2, and NMG 80, pH7.0, and a bath solution containing KCl 90, EGTA 2, MgCl2 0.5, and HEPES 10. Data shown for currents recorded at +100 mV used symmetrical solutions consisting of NaCl 130 mm, HEPES 3 mm, and EDTA 200 m, pH 7.2. Recordings were made with either an Axopatch 1D or an Axopatch 200 patch-clamp amplifier (Axon Instruments, Foster City, CA). Data were filtered at 2 kHz, and either an ITC-18 computer interface with Pulse data acquisition software (Instrutech, Port Washington, NY) or a DigiData 1200 (Axon Instruments) with our own software was used for voltage protocols and digital data acquisition. The long-time current records presented are strip chart recordings (Kipp and Zonen, Suskatoon, Saskatchewan, Canada). In all results presented, we define the CNG channel-mediated current as that current activated by 8-bromo-cGMP, cGMP, or cyclic inosine BIBR 1532 5-monophosphate (cIMP). Initially, we performed experiments with 8-bromo-cGMP under the assumption that this analog would not be cleaved by rod PDE. However, we determined that phosphodiesterase inhibitors could reverse effects of triphosphonucleotides in rod patches, whether submaximal concentrations.