The sensory seam: ionic sensors are sensory-cell transducers
A homeostatic comparator and a sensory-cell transducer are the same R19 instrument reading an ionic variable. CaSR (calcium), OTOP1 (acid/sour), ENaC (sodium/salt), ASIC and TRPV5/6 serve both interoception and an external sense; OTOP1 uniquely couples acid-base, calcium-carbonate otoconia, and gravity sensing.
The body's mineral, acid and electrolyte SENSORS are the same molecular instruments that sensory cells use for taste, balance and pain. A comparator in a homeostatic loop and a sensory-cell transducer are the same R19-class object reading the same ionic variable.
One instrument, two uses
| variable | systemic sensor | sensory-cell twin | instrument failure |
|---|---|---|---|
| Ca2+ | CASR (parathyroid comparator) | CaSR in taste / GI (calcium & kokumi taste) | ADH1 (CaSR gain-of-fn: defends too-LOW Ca) ; FHH (loss-of-fn: defends too-HIGH Ca) |
| H+ / pH | renal acid sensing + peripheral/central chemoreceptors | OTOP1 (sour taste) ; ASIC2/ASIC3 (nociceptor pH) | acid-base sensing failure contributes to mis-set ventilatory/renal response |
| H+ + CaCO3 biomineral | acid-base <-> mineral coupling | OTOP1 -> otoconia (CaCO3) pH-keeper | BPPV (dislodged/degenerated otoconia) -- a mineral-reservoir + instrument failure |
| Na+ | renal Na sensing (macula densa / ENaC) | ENaC (SCNN1A) amiloride-sensitive salt taste | Liddle (ENaC gain-of-fn: Na retention/hypertension) ; salt-taste loss |
| Ca2+ flux (effector) | TRPV5 (kidney) / TRPV6 (gut) Ca channels | TRP-family sensory channels (thermo/mechano/chemo) | TRPV5/6 dysfunction -> renal Ca leak / hypercalciuria (stone risk) |
Every measured sensor is a valid R19 instrument (all-valid True) with sharpness monotone in γ (True). Disease at a sensor is instrument failure: a mis-calibrated sensor defends a shifted setpoint, exactly the setpoint-drift mode.
OTOP1: the crown jewel
OTOP1 is a proton-selective channel that is both the sour-taste receptor and the keeper of the pH that forms otoconia — the calcium-carbonate biominerals of the vestibular organ. One molecule couples acid-base sensing, calcium-carbonate mineralization, and gravity sensing. BPPV (dislodged otoconia) is a common disease living at that mineral↔sensory seam.